After the restart issue (still not resolved) now phone shows a different problem. Sometimes, when a call comes or when i try to make a call the screen goes completely black. We cant see anything on the screen such time. Even screen wont respond if you try to cancel the call by touching the screen.
Since there is a proximity sensor, i thought this might be a problem caused by the tored screenguard and i got it replaced with a new one. For sometimes, it was OK. But still i am facing this issue every now and then. Infact, i have noticed that it is happening mostly when an another application runs in the background specially an application using networks connections such as e-mail, nokia maps, OVI etc....
However, after waiting 4 months, now i am decided to take this phone to the dealer and will discuss with them about these issues. Hope nokia will react to this kind of problems. It is definitely dissappointment for me....
I also have the same issue, I've restored to factory settings but the problem is still there. When I first got my phone It was working fine. It doesn't restart even if It has no signal, It just happened a month after I had the new software update... 
it's getting on me very bad... And then now, I can connect to wifi but It seems that It don't have an internet connection though out wifi has no Mac filter
