i have had my n900 since october last year and had no problems with it untill yesterday. i noticed i had no signal, so i rebooted the phone and got the error message 'sim card registration failed'

I have tried the sim in another n900 and it works, phoned vodafone to see if there was a block on the sim and they said everything is fine with it. I have reinstalled maemo with nokia updater, flashed it with the global firmware with maemo flasher, then reinstalled with nokia update, flashed it to the previous UK firmware then updated with nokia updater. still getting the same problem. i dont have the icon with the sim card with a cross through it in the system tray, and i get the same error from other sim cards, at this point i am thinking its a hardware fault, this is just a last ditch attempt to see if there is something obvious that i havent tried yet! any ideas guys?

update so far:
asked vodafone if they had blacklisted it, they said they hadn't. i sent it back to nokia who said tmobile had blacklisted it. i have never ever used tmobile on any phone. so i phoned tmobile to find out why, and they said the imei number is a n900 that was sold by tmobile and has been reported stolen and that i have been sold a stolen phone. i have had this phone since october 2009 and i bought it from new. they wouldn't even let me email a copy of my purchase order to prove its mine. so at the moment mobile phones direct are looking in to it. unbeliveable

Had the same issue when I was in the UK for Christmas. Luckily, it worked perfectly on my return to the US. Unbelievable happening!!

my original n900 broke in february, vodafone gave me a new one in april after finally collecting my old one. This n900 worked for 10days until i had the same error as you. after taking it into the shop 2times a week and ringing the customer service with vodafone GUARENTEEING it wasn't blacklisted they finally realised it was in September! and after taking 2weeks to sort it out it was then october, after using that n900 the charger port broke with in a matter of days. after 3 weeks of trying to get it repaired i was given a new device.

So far i've used just under 7months of the 13months i've paid for at £35 a month. and they won't give me a refund, the cheek of that!!!

How are all those numbers ending up in their blacklist? And why the police hasn't come knocking on your door after the carrier indentified you were in possession of stolen goods?

just had an email back from mobilephones direct to say the phone is not on the balcklist and i needed to contact vodafone. spoke with vodaphone and t-mobile who both confirmed it is still on the blacklist, spoke with mobilephones direct and checked what IMEI number they had for me and it was wrong. looks like mobilephones direct have messsed up when they where originally sending the phones out. they seem really unintrested about this and its all ways me chasing it up iwas told they are waiting for tmobile to get back to them as they had faxed the proof of purchase, which is obviously not going to help cause they have the wrong IMEI number. i am a very laid back person but this is winding me up, i just want to be able to use my n900!!