Change apn on 5.1.1
Need to get data on straight talk using iPhone 4 iOS 5.1.1 so I need to change the apn info
iPhone 4, iOS 5.1.1, Firmware 04.10.01
Take a look at this Apple doc -> iOS: About cellular data network settings (viewing or editing the APN)
You should be able to change the APN info from Settings > General > Network > Cellular Data Network.