I have a nexus one given to me by a friend who worked for google. He never used it, although told me it was unlocked.

I am running android version 2.3.6, and I am up to date for everything.

I have tried with two different prepaid sim cards across 4 different countries, 3 in the EU and Israel.

In all cases when trying to join a network I just get error in searching for mobile networks. How can I fix this and use my phone as a phone?