I’m looking for some technical assistance with a persistent calling issue on my Samsung Galaxy S24 Plus.
The Problem: Specific callers on the O2 network are unable to reach me. When they call, they hear an automated message stating, "The person you are calling is on another line," even when I am not on a call.
What I’ve discovered:
If I disable "Block calls from unknown numbers" on my S24 Plus, the calls successfully come through.
However, even when the call comes through, it displays as "Private Number" rather than the contact's name/number.
If the O2 caller prefixes my number with *31#, the call comes through perfectly with their Name and Number displayed.
Troubleshooting already completed:
Verified no call diverts or forwarding are active (##002# cleared).
Toggled Call Waiting off/on in Supplementary Services.
Toggled VoLTE and Wi-Fi Calling settings.
This is not a "blocked contact" issue, as it happens even if the contact is deleted and re-added.
It is isolated to specific O2 users (both on iPhone and Android).
Technical Conclusion: It appears there is a CLI (Caller Line Identification) Stripping issue occurring at the interconnect gateway between O2 and Three. The O2 number is being dropped during the handshake, causing Three to deliver the call as "Private." Because my phone is set to block unknown numbers, it auto-rejects these calls, triggering the "on another line" message for the caller.
Since *31# (Force Caller ID) fixes the issue, this seems to be a network-level routing or IMS profile mismatch rather than a handset fault.
