Can't use gsm codec with SIP protocol

I have installed latest asterisk 1.6 on freebsd 8.1.
I want to make some tests, but i can’t use gsm codec with SIP protocol. I try’it x-lite 3.0, 4.0 and zoiper as softphone, with same result.
I receive this in log:

NOTICE[9899] chan_sip.c: No compatible codecs, not accepting this offer!

sip.conf allow only gsm codec.
With iax2 protocol, codec work well.
Is there an problem with asterisk on freebsd or something more general?

Hi

You need to check your sip peer setting to make sure you have allowed GSM and check the softphone as well

Ian

I check that.
Into sip.conf allow gsm and ulaw. In softphone allow only gsm codec.
I forgot to mention that it goes well with IAX protocol.
In console erorr is this (if help)

chan_sip.c:8508 process_sdp: No compatible codecs, not accepting this offer!