This affects SIP2SIM customers who would previously have seen short CLI on calls to their SIM - eg where an incoming call to the SIM would have shown the short extension number of a caller on the same PABX.
Our SIP2SIM service is intended to allow a SIM in any phone or any 'dumb' phone to work as a SIP extension, either a SIP number provided by A&A or an extension on a customer's own SIP PBX. This meant that, for example, for an internal call, you would see the call from that internal extension number. This was not perfect, e.g. a call from extn 401 might show as +401, but it worked.
A change in Ofcom policy has meant that we now have to send a 'valid' looking CLI SIM. This is fine for normal calls from 'outside' your PABX as they will have the proper CLI of the caller, but customers running their own PBX may well be using short extension numbers, and 'internal' calls on the customer PBX between extensions would be sending the extension number as the CLI. eg a three digit extension number such as 402 or 403 etc.
In situations where an invalid CLI is used - eg an 'internal' call to the SIP2SIM extension, we have to now change the CLI to look like a 'valid' CLI.
Our workaround is to change the CLI to be: +11, then a number of zeros, then the original CLI requested, so +11 and 9 further digits.
eg, if you have two 'internal' extension numbers, 402 and 403. 402 is a normal SIP phone, and 403 is registered from a SIP2SIM. A call from 402 to 403 will have the CLI changed to: +11110000402
This does mean a call back to such a number would hit your PABX with this otherwise invalid number. We suggest you make your PABX map these to internal extensions if possible.
This does somewhat break the philosophy of our SIP2SIM service as a SIM being a normal SIP extension. We are not happy about this. This change is mandated by Ofcom and we have no choice.