i cant even find the network option on i os 6

If the iPhone is carrier locked and the carrier doesn't provide or need the option, it won't be available.

Depending on the Carrier you are using the Settings may not show up. You can go to http://www.unlockit.co.nz from your iPhone and choose your Country and Carrier and it will set the Correct APN Settings for your Carrier.

my conract is over with at&t and i just bought a straight talk ,my iphone 4 doesn't have cellular data network option. i went to http://www.unlockit.co.nz/ and set apn. but picture message doesnt work. can you help me pls