Okay, so it sounds as though it's not a memory leak in Maemo. A reboot would cure that. A loose cable that runs between the display and keyboard sections of the N900, perhaps? This might support Texrat's memory leak theory. Rebooting (or shutting down and restarting) an N900 completely restarts Maemo, thereby correcting the damaged caused by any memory leaks there. However, I don't know whether or not a reboot also causes the GSM processor to restart. It could be that the GSM processor maintains its state through a phone reboot. Pulling the battery, either to replace the battery itself or the SIM card, would force the GSM processor to start anew though. Does pulling the battery get your phone working again (at least temporarily) every time? There's a small backup battery or capacitor inside N900s to help them retain settings (such as date and time) through battery changes, so you may need to keep the battery out of your N900 long enough for that to drain. A minute or two should be more than enough.