Just updated to PR1.3 some days ago. All worked fine before the update, but after, I've had big problems with the SIM card "disconnecting". That is, the 3G symbol and signal strength disappears, and after some seconds, a SIM card with a red cross shows. It always manages to reconnect after a while, but I can't send or receive e.g. SMS when this happens.

It seems to be related to data transfer. It usually happens when I send or receive an SMS, but not always.

The only coommunication apps I have are fMMS and Firefox.

Any idea what could be wrong?

i've noticed same thing but only once. i guess it is related to low signal or low 3g signal while a network connection is active

No, I get this problem pretty much everywhere, and it has never happened earlier. The signal is 100 % in many cases. Anyway, it shouldn't show up as disconnected SIM card!

Was your update OTA or a .bin total reflash?

When this happens type *#06# in the phone to see if you have an IMEI number, if you don't it could be a hardware issue.

A missing IMEI number shows a SIM card symbol with a red line through it and you cannot even make emergency calls! This happened to me 2 months ago, it meant sending the phone off to Nokia for a replacement.

I have the same issue but it only happens with my second battery (cheap no-brand immitation). It never happens with the original OEM battery that came with the N900.

My guess is that it has to do with voltage fluctuations or something because that battery also goes from half full to empty in a matter of a minute or two and that's when I get the problem you describe - also usually when a call/sms comes in or when I try to make a call or send an sms.

This happened with me in PR1.2 but after a while it just stopped. Hmmm

Ele-Mental: Updated through the application manager.
JonWW: Yes, I do have an IMEI.

Additional information: When sending or receiving SMS and such, the signal often drops from 3.5/3G to 2.5/2G.

bfritsch: I have the original battery. I'll try to remove battery-eye, perhaps that could cause problems? Come to think of it, I recently updated that too...

I would recommend doing a backup of your settings with the backup app, copy all your data off the internal drive, then trying a re-flash with both bin files, this will return your device to factory new state.

You will need to follow the instructions in the Wiki to do this, unfortunatly the download link for the device firmware is down at the moment.