What is caller ID?
Caller ID is the number that appears on the display when someone calls. On an outgoing call from the PBX, you choose which number the other side sees — usually the business's main number, not the extension number or a private mobile.
Two directions of the same thing
The professional term is CLI — Calling Line Identification. In an ordinary call we think of it from one side only: who is calling me. In a business it has two sides, and both are equally important.
- On an incoming call — you see who is calling you. This lets you answer by name, know in advance who is on the line, and route the call according to the caller.
- On an outgoing call — the customer sees who is calling them. This determines whether they will answer, and where they will call back if they did not.
Many businesses invest in the incoming side and forget the outgoing one. But a customer who sees an unfamiliar number simply does not answer. And a customer who calls back the number that appeared and reaches the mobile phone of an employee who has already left is a customer who got lost.
How the number travels with the call
The number is not "discovered" by the other side. It is sent together with the call, as part of the information that sets it up. In calls over an IP network, in the SIP protocol, the number is in the headers of the message that opens the call. On many analog lines it is sent as a short signal between the rings — which is why on old phones the number appeared only after the first ring.
On a call that goes out of a PBX, the PBX decides which number will be sent. It does not send the extension number (201 means nothing to a customer outside), and not the number of the device that was dialed from. It sends the number that was set for the extension.
And what about a name? In most cases in Israel the network passes only the number. The name that appears on the display comes from the contacts on the other party's phone. So it is worth encouraging regular customers to save your main number.
Which number to display on an outgoing call
| Option | When it fits | What happens when the customer calls back |
|---|---|---|
| Main number | Most businesses, most employees | Reaches the menu and from there every department |
| Department number | Sales, billing, service | Reaches the right department directly |
| An employee's direct number | Account manager, advisor, personal coordinator | Reaches the same person |
| Withheld number | Special cases only | Nowhere to call back |
The simple rule: display a number that has an answer behind it. If a billing employee calls customers, and the customers call back a number that leads to a general menu — they will complain that they cannot reach her. A direct billing number solves this.
About a withheld number: many people do not answer a withheld call, and some institutions and phones block it. For an ordinary business it is almost never a good choice.
Mobile, SIM and app: protecting privacy
Here caller ID becomes a personal matter. An employee who calls a customer from their personal mobile exposes their number. From that moment the customer will call them directly — in the evening, on vacation, and even after they leave the job.
A PBX solves this. A SIM extension or an app on a mobile phone behaves like any other extension: the call goes out through the PBX, and the customer sees the business number. The personal number is not exposed, and callbacks reach the business — the queue, the menu or the employee's extension, according to the setting.
Example: a nonprofit fundraising coordinator works from home and from the car. He calls donors from his mobile, through an extension. The donors see the nonprofit's number, and when they call back — the call reaches the nonprofit and not his personal mobile.
On an incoming call: what to do with the number
The caller's number is not just a display. It is information you can work with:
- Routing — routing by caller sends a regular customer straight to their agent, or a caller from abroad to an English-speaking team.
- Preparation — the agent sees on the display who is calling, and sometimes also which line or queue the call came from.
- Documentation — in the call log every call is saved with the number, so you can search all the calls of a specific customer.
- CRM connection — a CRM system identifies the customer by the number and opens their record.
And what happens when the caller is withheld? Then there is no number to work with: you cannot route by it, you cannot call back, and the log will record a call without a number. This is why many call centers ask a withheld caller to leave a callback number in a message, or route withheld calls to a general queue and not to a personal agent.
It helps even in a small office: a secretary who sees on the display that the call came through the donations line and not the main number answers "Donations line, hello" — and the caller feels they reached the right place from the first word.
Number spoofing and why you cannot display any number
Technically, whoever controls a PBX can try to send any number they want. This is exactly what spam callers and fraudsters do: they display the number of a bank, a government office, or a number that looks local, so that people will answer. The phenomenon is called caller ID spoofing (Spoofing).
Because of this, providers and well-run PBXs allow displaying only numbers that belong to the organization. This protects you too: nobody else can call your customers with your number. If you need to display another number — add it to the account, and do not "invent" it.
Pay attention to the other side too: if a customer reports a call "from you" that did not come from you, someone may be spoofing the number. This topic is also related to telephony fraud.
Practical tips
- Choose an outgoing number for each extension on purpose, not only by the default.
- In a dialing campaign, display a number where whoever calls back hears an explanation or reaches an agent — not a number that rings into the void.
- Check from time to time: call your own mobile from each type of extension, and see what appears on the display.
- When an employee leaves, their extension stays in the organization — and so does the number the customers saved.
What each extension type displays — the full table
The question "what does the customer see" sounds simple, but the answer depends on where the call came from. Here is what happens with each type of extension, when it is set up correctly in the PBX:
| Where the call comes from | What the outside customer sees | What a colleague sees on an internal call |
|---|---|---|
| IP phone on the desk | The number set for the extension — main, department or direct | The extension number and its name |
| Softphone on a computer or an app on a mobile phone | The same: the number set for the extension. The personal mobile is not involved | The extension number |
| SIM extension | The business number. The call goes through the PBX | The extension number |
| Forwarding to an external mobile (Follow Me), when the employee calls back from the mobile itself | The mobile's personal number — because the call did not go out through the PBX | — |
| Calling card from a shared station | The number set for the station or the card, not the student's number | The station number |
| Dialing campaign | The number set for the campaign | — |
| A call transferred from agent to agent | The customer sees no change | The receiving agent sees the original customer's number |
The row where the most people go wrong is the forwarding-to-mobile row: when the PBX forwards an incoming call to an employee's mobile, it works well. But if the employee returns the call from their own mobile, without going through an extension — the customer sees the personal number. The solution is to call back through an app or a SIM extension, and not from the regular dialer.
The anti-impersonation rule: only numbers registered in the account
It is worth understanding this rule in depth, because it determines what is and is not possible. A well-run PBX keeps for each account a list of registered numbers: numbers that were opened in it, and numbers that were ported into it. Only a number from this list can serve as the outgoing caller ID for an extension. A number that is not on the list — cannot be chosen at all, and an attempt to send it another way is blocked or replaced with the account's default number.
What does this mean in practice?
- A number opened with us or ported to us — available immediately to every extension.
- A number you have with another provider — no. As long as it is registered there, the PBX here cannot display it. The way is to port it, and then it is yours for caller ID as well.
- An employee's personal mobile — no. It is registered with the cellular company in the employee's name, not in the business account.
- A number you saw in an ad — certainly not.
The rule sounds restrictive, but it is exactly what protects your number: just as you cannot display the bank's number, nobody can display yours. In phone networks around the world, verification mechanisms are also developing that check on every call that the displayed number really belongs to whoever sent it, and mark a call that did not pass verification. As these mechanisms spread, a call that goes out from a number registered in a well-kept account will look more trustworthy than a call from an "improvised" number.
Pay attention to the order of actions in setup too: you choose the outgoing caller ID for an extension after the number is already in the account. A business that ports its main number next week cannot display it today — until the porting day the extensions go out with another number that is already in the account.
When something does not work: symptom, cause, solution
| What the customer sees | Common cause | What to do |
|---|---|---|
| "Withheld number" or "Unknown" | No outgoing number was set for the extension, or a number that is not in the account was set | Open the extension in the control panel and choose a number from the list |
| A number of another department | The extension inherits the account default | Set it on the extension itself, not only on the account |
| The employee's personal mobile | The employee called from the regular dialer and not through the app or the SIM extension | A short briefing: work calls go out only through the extension |
| A "suspected spam" warning on the customer's mobile | Caller ID apps on mobile phones flag a number based on user reports, mostly after many short unanswered calls | Display one fixed number over time, do not swap numbers between campaigns, and make sure whoever calls back that number gets a real answer |
| The name of another business | The number used to belong to another business, and the customer saved it that way in their contacts | Ask the customer to update it; it fades over time |
The fastest way to check: one extension of each type calls your mobile, and you photograph the display. Five minutes, once a quarter, and this whole table does not stay theoretical.
How it works with us at Kesher
In the control panel you set, for each extension, which number is displayed on outgoing calls, from among the organization's numbers. All employees can go out with the main number, a department can go out with its own number, or a specific employee can go out with a direct number.
SIM extensions and apps go out with us under the business number. The employee dials from the mobile, and the customer sees the organization's number — so the personal number is not exposed, and the callback reaches the business. A SIM extension works without an app and without data, and so it also suits a kosher phone.
On incoming calls, agents see in advance which number the call comes from and which line. On the "Numbers" screen you can set routing by caller, and in the call log you can search by number and see all the calls of the same customer.
Want to check what customers see, or change the outgoing number of a whole department? You can do it yourself with the illustrated guide, or ask us.
FAQ
How do I hide my personal number when calling for work from my mobile?
Dial through a PBX extension — a SIM extension or an app. The call goes out with the business number, and the personal number is not displayed.
Can I display someone else's number on an outgoing call?
No. Only numbers that belong to the organization can be displayed, to prevent impersonation.
Why don't customers answer when we call?
Often because the number that appears for them is unfamiliar or withheld. Displaying the main number, which customers know, improves the answer rate.
Does the business name appear on the customer's display?
In most cases only the number is passed. The name appears if the customer saved the number in their contacts.
What is the difference between CLI and Caller ID?
There is no practical difference. CLI is the professional term in phone networks, and Caller ID is the familiar name for the same thing: the number that appears on the display.
Why do I see 201 on a call between extensions and not the business number?
On an internal call the PBX displays the extension number and its name, because that is what helps a colleague. The business number is sent only when the call goes out to the network.
Our number is marked as spam by customers. What do we do?
The marking comes from caller ID apps that rely on user reports. Display one fixed number, do not dial irrelevant numbers at machine speed, and make sure that whoever calls back the number reaches a person. Over time the marking fades.
Can I display our local number abroad?
If the number abroad is registered in your account, in most cases you can choose it as the outgoing caller ID for an extension, like any other number. Some countries have their own rules, so check in advance by country.
An employee calls customers from their personal mobile. How do we prevent exposure?
Give them a SIM extension or an app, and explain that every work call goes out through it. The call passes through the PBX and is displayed with the business number; the mobile's regular dialer stays for private calls.