Straight talk iphone 4s internet not working?

I just bought an iphone 4s unlocked from online and i took my straight talk phone sim card and cut it into a micro. So it can fit my iphone and everything works fine, but my internet isnt working and all it says at the top is HOME G.

The iPhone wifi is totally separate from the SIM card.
Go into Settings: Wifi: and enable

Is there any warranty on it? You can bring it back to them and tell the issue if there is no warranty you have to go to mobile services to fix it.