Did you update to PR1.3 "over the air"? If so, then a re-flash might help (see http://wiki.maemo.org/Updating_the_firmware). If you updated via your PC then you've already re-flashed it.

If that doesn't fix it, it's probably the hardware - back to Nokia. At least being in Helsinki you should get good service

There's also a (small) chance it could be your operator - or maybe a SIM card problem.