Hi, I live in Costa Rica and I purchased a Nokia N900 in Amazon (the US Version with full guaranty), I entered all of my contacts and when I made a phone call to one of them the phone shows the image and phone number but the problem is when one of my contacts call me back in the screen the phone shows a message "Unknown number" even when the number is already in my contacts or I have called the contact before and when I tried to call to the "unknown number" as displayed in the phone function it shows another message "Call not allowed". I entered the numbers with country code +506 and without country code but it has not display the contacts yet (we do not use area code).
Do you know how to solve this? Thank you.

seems not u' problem, but u' friend or the carrier barred the caller ID so # isn't displayed in u' phone.

can u show u' friend # on another phone?

Try to check if you do not have doubled your contacts, than the phone do not recognized none of them. In my n900 I had two equal numbers and could not browse them from phone app.

Finally I know how to display the incoming calls. I went to ICE (Which in Costa Rica is in charge of bring GSM services like AT&T and Verizon), and they change my old Sim Card (GSM) of 2003 and provided me with a new one and that's it problem solved.

Hi!

I live in CR too and had the same problem. Just needed to change the SIM and that's it.