Hi!

I also had lots of problems with my SIP phone on N800.
First I could not make any outgoing calls. The solution for this problem is already described in this forum (thanks for that!).
Now I have a problem receiving calls on my SIP number.
Generally I think this SIP feature is still not mature on N800. Here is what I found:
1) The other applications like Skype and Gizmo obviously affect SIP functionality
2) If you have Skype installed on your N800 then do the following:
a. Stop Skype
b. Disconnect SIP connection (green button in status area)
c. Start Skype and connect to the server
d. Connect again SIP connection (Red-white button in status area)
e. Now you should be able to receive calls on you SIP number
f. Unfortunately it works only for a while. After some time it seems that the server lose the client again
3) If you have Gizmo installed, then it is even more complicated
a. Then you should disconnect SIP connection first (green button in status area)
b. Start Gizmo and connect to the server
c. Disconnect Gizmo from the server
d. Connect again SIP connection (Red-white button in status area)
e. Now you should be able to receive calls on your SIP number

I would appreciate if you can make your comments here if the SIP behavior is the same on your N800. May be we can find solution how to bring it work permanently.

Are there any possibilities to report bugs directly to Nokia?

Anyway I think Nokia did quite a good job offering great communication features for N800. May be the next OS 2008 update will fix this problems.