Caller ID Not Showing on VoIP Calls? How to Fix It

When your business calls display "Unknown" or "Withheld" instead of your company name and number, it undermines trust. Customers are far less likely to answer calls from unidentified numbers — some studies suggest up to 87% of unknown calls go unanswered. For sales teams, support departments, and any business that relies on outbound calling, broken caller ID is a serious problem.

This guide covers every reason your VoIP caller ID might not be displaying correctly and what you can do about it.

How VoIP Caller ID Works

Understanding the system helps you fix it. VoIP caller ID has two components:

• Calling Number (CLI — Calling Line Identification) — the phone number displayed to the person you are calling. This is set in your VoIP account or phone configuration.
• Calling Name (CNAM) — the business or personal name displayed alongside the number. How this works depends on the receiving carrier and their database lookups.

For outbound calls, your VoIP provider sends your CLI in the SIP headers. The receiving carrier then decides whether to display it, modify it, or block it based on their own rules and validation checks.

Reason 1: CLI Not Configured in Your VoIP Account

The most basic cause — your outbound caller ID simply is not set up.

How to Check

• Log into your VoIP provider portal or admin dashboard
• Navigate to your number management or caller ID settings
• Check that an outbound CLI number is assigned to your account, user, or trunk
• Ensure the number is in the correct format (typically E.164 format: +44 followed by the number without the leading zero)

How to Fix

• Set your main business number as the default outbound CLI
• If you have multiple numbers, assign the correct CLI to each user or department
• Some providers let you set different CLIs for different call routes — check this is configured correctly

Reason 2: Number Not Verified or Validated

To prevent fraud and spoofing, VoIP providers and carriers increasingly require that outbound CLI numbers are verified as belonging to you.

What This Means

• Your provider may require you to prove ownership of the number you want to display
• Numbers ported to your VoIP provider usually verify automatically
• Numbers from external sources may need manual validation
• Some providers will not allow you to display a number that is not on their platform

STIR/SHAKEN and Call Authentication

The telecoms industry is implementing call authentication frameworks. While STIR/SHAKEN is primarily a US standard, the UK is moving toward similar validation. Calls that fail authentication checks may have their caller ID stripped by the receiving carrier. Ensure your provider supports these protocols.

Reason 3: Phone or Softphone Override

Your handset or softphone application may be overriding the account-level caller ID setting.

• Check phone SIP settings — some phones have a "Caller ID" or "Display Name" field that, if populated, overrides the provider setting
• Check for "Anonymous" settings — some phones have a "Hide Caller ID" or "Anonymous Call" option that suppresses your number
• Softphone applications — apps like Zoiper, MicroSIP, or your provider own app may have caller ID settings that override the server configuration

Reason 4: Carrier-Level Blocking

Even if you send the correct caller ID, the receiving carrier may not display it.

Why Carriers Block Caller ID

• Spam filtering — if your number has been reported as spam (even incorrectly), carriers may suppress it
• Invalid number format — numbers sent in non-standard formats may be stripped
• Geographic mismatches — displaying a UK geographic number while calling from an overseas IP address can trigger fraud filters
• Mobile carrier policies — some mobile networks display caller ID differently or apply their own CNAM lookups

What You Can Do

• Check whether your number appears on any spam databases (there are free lookup tools online)
• Ensure your number format is correct and consistent
• Use a number that matches your business geographic location where possible
• Ask your VoIP provider to check the SIP headers being sent for your calls

Reason 5: Number Porting Issues

If you recently ported your number to a new VoIP provider, caller ID issues are common during and shortly after the transition.

• During porting — there can be a period where the number is in limbo between providers, and caller ID may not display correctly
• After porting — it can take 24-48 hours for all carrier databases to update with the new routing information
• CNAM updates — even after porting, the calling name associated with your number may still show the previous owner details until databases refresh

If you have recently ported, give it 48 hours. If caller ID still is not working after that, contact your new provider.

Reason 6: Using the Wrong Number Type

Not all VoIP numbers work the same way for outbound caller ID.

• Geographic numbers (01/02) — generally display correctly on all networks
• Non-geographic numbers (03) — should display, but some older systems may not recognise them
• Mobile numbers (07) — may not be available as VoIP CLI depending on your provider
• Toll-free numbers (0800/0808) — usually cannot be used as outbound caller ID

If you are having persistent caller ID issues, try switching to a standard geographic number as your outbound CLI.

How to Test Your Caller ID

Before assuming there is a problem, test systematically:

1. Call a mobile phone — check what number and name appears
2. Call a landline — some landline networks display caller ID differently
3. Call a different mobile network — test on EE, Vodafone, Three, and O2 to see if the issue is network-specific
4. Check your SIP headers — use your provider call logs or a tool like sngrep to inspect the actual SIP INVITE message and verify the From and P-Asserted-Identity headers
5. Ask your provider for a test — they can often verify what CLI is being sent from their platform

Setting Up Caller ID Properly

For the best results across all networks:

• Use a verified, ported geographic number as your primary outbound CLI
• Ensure number format is E.164 — +442012345678 rather than 02012345678
• Set the display name in your provider portal to your business name
• Configure at the account level rather than per-phone to ensure consistency
• Register your number with CNAM databases if your provider offers this
• Avoid changing your outbound number frequently — consistent use of the same CLI builds trust and reduces spam flags

For a comprehensive look at choosing the right VoIP solution that handles caller ID setup as part of the service, see our hosted VoIP solutions guide.