Lucas,
Check the following
• Power off the phone, then power it back on. If it is working properly, it should ask "Continue in offline mode yes/no?"
• Check SIM card to see if it is properly seated. You may have a damaged SIM card slot?
• Check to see which profile your phone is set to. There are a few modes that put the phone offline.
@oldturkey03 -- N70 is a good old fashioned Symbian S60 OS based phone. Offline mode means its disconnected from the Cell Network.