I currently live in the UK and I try to use Phoner and/or Fritzbox 7170 via TESCO ISP.
I believe I have the Phoner properly configured as I can register at the TESCO registrar. 
I can also receive calls. Whilst receiving calls the codecs are for  IN: A-Law and for OUT: A-Law.
However, when I try to establish an outgoing call it does not work and the following occurs:
1. registered -OK-
2. dial the outgoing phone number
3. outgoing phone rings
-- whilst ringing I can see green bars on the 'receive' and 'transmit bar in the Phoner
4. picking the outgoing phone up
-- line seems to be dead
-- still green in transmit bar
-- NO codecs  for IN and OUT
-- can't communicate via the established line.

If I use TESCO's own Softphone all calls work fine. I almost think that they somehow manipulate the SIP session initiation or the RTP channels. 
I run also a trace with WireShark and I could see that the TESCO proxy uses port 5070 for the establishment of the call with the TESCO Internetphone, whereas port 5060 is choosen for the Phoner.

Your help would be realy appreciated. - Best regards....

Hello,

I am using PhonerLite 1.63. 

As I am NEW to the world of 'forums' could you please let me know on how to send the traces to you. 
The trace I have contains also sensitive information - which should perhaps not be publicly available.

When the connection works (via Tesco softphone) the ILB codec is used.

Cheers