T23P + Asterisk 11 + SIP Provider -> No voice on call to specific mobile provider

[nsarris]

Hi,

I've been using yealink phones for years and I've stumbled upon this very wierd issue.

We just reveived our first bunch of T23Ps. We are using asterisk 11 (FreePBX) and a greek SIP provider (CYTA) for outbound calls. Every yealink phone works fine EXCEPT for the T23Ps that have no voice ONLY for calls to a SPECIFIC mobile provider.

For example

T20P/T26P/T28P ->Any number : works
T23P->Asterisk->Land lines : works
T23P->Asterisk->Vodafone mobile: works
T23P->Asterisk->Cosmote mobile: no sound

We talked to our SIP provider and they couldn't trace anything after the calls left Asterisk (which is expected)

In our internal traces nothing seems to be different between the working and non working calls (traced both Asterisk and SIP packets).

There is no NAT or network routing invovled (asterisk and phones on same subnet)

We tried all possible codec combinations (also tryied using different codecs on trunk and phone to force transcoding)

We couldn't get it to work... Any ideas?