I have a NOKIA N900 for past 5 Months and am facing issues from day one. I am really getting feed up with this Nokia N900. I feel if the issue is with the phone or with T Mobile. I had this phone replaced from Nokia Service center and was hoping that the replaced phone set works. Both the older set and the replaced ones have got the same issues. Now I really doubt if there is an issue with the phone or with T Mobile. Here is the list of issues that I am facing with Nokia N900.

1) Multiple Call drops: I am facing Call drops issues whenever I am on a move. I do not remember an instance when I was able to complete a call while travelling.
2) Signal Lost when I change orientation: On changing the display Orientation from Landscape to Portrait, I lose he signal bars and an error message displayes "No SIM card Inserted".
3) Multiple Reboot required for starting NOKIA N900: Never able to start Nokia N900 in a single attempt.
4) Nokia N900 shuts down on its own whenever I am surfing Internet. This issue has started to happen recently.

Please do let me know what I should do now. I am running out of options. Please help me out.