Uable to locate Iphone configuration on my 3.1.3 this is the first I phone made where and how canan I find this information

I cannot locate the IPhone configuration menue on the Iphone 3.1.3 I have unlocked my phone have a straight talk Sim it works not able to get on line no. Popup No data service I need to change the apn . I can go to settings then general then network I get 3 choices Data roaming on off , VPN on off, WI_FI on off where do I find network configuration. Help!!!!