I just bought a blackberry off my friend and when I put my sim card in the phone I get a message that says sim card error. I can make calls and use the direct connect to others but cant add my address book or get on the net. my other phone was a i860 and my data worked and everything else.

Please help..

Not all SIM cards are created equally. That SIM card probably isn't compatible.
Some SIM cards will not allow you to use certain features of the Blackberry.
Contac Sprint/Nextel and see if they can get you a SIM card for the 7100i.

The data that worked on your i860 is not the same at the data plan for the BB. You need to buy a BB data plan to be able to go on the internet and get email on your 7100i.