T-Mobile Network.  Most reliable.  Strong Signal.

Unlimited Talk Text & Global Text (text anywhere in the world) Just $40 a month

$60 a month will get you unlimited DATA.  Data can work on an unlocked iphone.

Works with Any T-Mobile or any Unlocked GSM Phone

Here is a video of how to setup your iphone for simple mobile internet
http://www.youtube.com/watch?v=jmB6cdJUYv8