Hi iTor, big thanks for your interest, I thought this thead had fallen into a deep pit.

Sorry reinob, I didn't get your last answers, and I thought this was a dead end.

I still haven't solved my problem, so I'm using an ancient Nokia 3120 until I can fix this.

My n900 works with Movistar, Vodafone and Orange, but it doesn't work with Yoigo SIMs, I have tried 4 different SIMs with no joy.

I have contacted Nokia Care in Spain this morning, and I've been speaking with a very nice agent (thanks Carlos) who has plenty of N900's for testing, so I think he'll eventually come up with a solution, so I just sent him a link to this thread.

I don't think this might be related to the sim reader, as I get no errors during PIN verification nor network registration, and netmon correctly displays the registered network, both in GSM and 3G, but I'll have a look at those links anyway, thanks for pointing them out.

I'll update this if I ever find a solution, I still haven't lost my hope.