T58A outgoing call problem

[al552]

Hello
I've got a problem with configuring my new T58A. I'm trying to setup it using typical providers manual (editing only server host, username, password).
It worked fine with mobile sip softphone apps, with new DECT base Yealink W60B and Yealink CP960.

I got stuck with outgoing calls to any mobile phone or other not-corporate phones. Every time I get "Internal server error" message on T58A display. Any other device easily connects to client.

I can call to my coworkers via internal phone numbers but not to clients external phones. I tried to load defaults and re-enter credentials (twice), tried to use active user's credentials and checked those "problem" credentials in other sip-phones. Also tried to upgrade T58A firmware to the latest 58.83.0.5. Tried to compare settings of T58A and CP960. All those methods doesnt work. And of course I asked my sip-provider's support for help.

Current FW for T58A is 58.83.0.5 HW 55.2.3.0.0.0.0
Current FW for W60B is 77.81.14.1
Current FW for CP960 is 73.80.0.45

The last chance is to test device with other sip-provider. And if it will not work - visit store for guarantee.

Can anybody help me? Maybe I forgot something to check.