Well, it's an IP phone (PingTel) but what i did to resolve the pb is that I comment the lines:
maxexpirey=180
defaultexpirey=160
defaultexpirey=160
in the 'general' tag of sip.conf file. Now, I haven't got this error anymore and the communication is OK... It sounds good like this!
�^�+$Rǫ�f��)��+-�^�+$Rǫ�X���b�+�r�����X���b�+�r���������+-�w���-z���� ���PԔ � (��]jר�ب���+a���X���b�+�r���������+-�w���-z���� �
