Same issue here in Malaysia. My N900 would persistently "internet connection failed" until I restart the unit.

Previous round was so bad that it didn't even display the operator logo. But after restarting everything behaves as normal.

I have been an avid Debian user for a couple of years, hence my affection of a debian-relative n900/maemo. Upon coming up on this problem, I am seeking ways to restart the cellular data subsystem without going through the hardware restart/poweroff and on, but have not located it. In debian, there is almost a way to call the /etc/init.d/service restart script to restart the relevant process without having to bring down the whole system which could be running for months on ends.