Hello Elior,
welcome to the Polycom Community.
It is always useful to include the currently used SIP or UC Software version as issues experienced may already be addressed in a newer release.
This also allows yourself and others to check against current software release notes.
The above is also stated in the "Read First"
Therefore the Polycom VoIP FAQ contains this post here:
Question: How can I find out my SIP UC Software Version or the BootROM Version of my Phone?
Resolution: Please check here
In addition did you check:
Oct 7, 2011 Question: Can I register or is my Polycom Phone compatible with a “XYZ” SIP Server?
Resolution: Please check => here<=
and did you try to troubleshoot looking at :
Jan 19, 2012 Question: How to troubleshoot Polycom VoIP related Issues?
Resolution: Please check => here <=
Please ensure to provide some feedback if this reply has helped you so other users can profit from your experience.
Best Regards
Steffen Baier
Polycom Global Services