how can i change my apn on my iphone 3gs

http://support.apple.com/kb/HT4839

Iphone Config. Is it possible or are there plans to open the Config to access the following fields? ie Proxy, MMSC, MMS and MMS Port. The others are set and my IPhone is able to access everything but picture messages. I have submitted a request for att to "unlock" my phone. Will that allow me access to these other fields?