Cannot auto select carrier or make and receive calls

jonkey

Got an iPhone 4S from a friend who got it from a friend so the origin of the phone is very unclear in terms of network. It is locked, I was told by apple, to 3 so i got a 3 sim and the phone operates perfectly, I can send messages and often able to use mobile data (although poorly). When I attempt to make a call it just beeps out and I cannot receive calls. Also, when I go to the carrier option in the settings and attempt to switch it to auto, i'm left with no service until i select 3 manually.

Can anyone give me a reason for this and maybe a solution? Will unlocking it rid it of these problems?

Thanks