Ah, well, I have been asking around and it seems nobody has a yoigo SIM in the office. Sorry about that.

Very strange problem indeed. Please keep us updated, Ramoncio!

/Estel

I'd like to close this thread with a last update.
I sent it back to Nokia for the second time (the first time they didn't do anything at all, and sent it back as it was) and they told me that it was IMEI blocked by Yoigo, or something like that, as if it was (maybe) stolen!
It might, as I got it from eBay from a guy from Benidorm.

@ramoncio,

Wow. Sorry about that!

I'm not sure if it's possible at all to modify your IMEI by software. If so, you could buy a cheap Nokia, reprogram your N900 with the new Nokia's IMEI and then bin the cheap Nokia.

I have some old nokias in a drawer, I didn't think about changing the imei, good idea.

But don't be worried for me reinob. Last month I changed to a new phone provider (Jazztel movil), and now the N900 works fine.

In fact I've been even thinking about the option of using it as my main phone and sell my SGS2, which I've been using as main phone for nearly a year, as my n900 didn't work with Yoigo.
But there are a few deal breakers that are keeping me from that:
- Teamviewer - more router friendly than vnc
- Whatsapp - most of my friends use it. I'm trying yappari now, but it doesn't seem to register.
- Viber - a few very good friends use it
- UFC.tv - I like MMA
- Lack of app development, compared with other big ecosystems. What happened with alien dalvik?!?!
- Nice big super amoled screen
- power and speed

So I think I'll keep them both, SGS2 as main phone and the n900 for work, as a small laptop with 3G/wifi data connection to my linux servers.
And my next phone will have hdmi, so I can use it with ubuntu for android. http://www.ubuntu.com/devices/android
Maybe Sony Xperia acro S, rugged but very nice.

By the way thanks for keeping up with the thread!