Help with my samsung eternity?

[Misty]

I just bought a samsung eternity from a friend. when i stuck my sim card in it lets me recieve texts but it will not let me send them. it says network connection unavailable. it has 2 bars where i live. is it supposed to say 3g or something at the top? am i missing something? i still dont seee how i can recieve them but not send them....can anyone help me please. o and i have a go phone sim card going into a regular at&t phone if that makes a difference