There are several ways to problematically detect if an iPhone has an internet connection, but most of them cant tell you how the iPhone is connected to the internet.

Apple has sample code to accomplish just this task. The Reachability class is not shipped with the SDK, but is part of a sample project of the same name. http://developer.apple.com/iphone/library/samplecode/Reachability/index.html

Using the reachability class:

Set up:

• Download the reachability project from Apple
• Copy Reachability.h and Reachability.m to your project.
• Add the ‘SystemConfiguration’ framework to your project.

Sample Usage:

Reachability *reachability = [Reachability sharedReachability];
 [reachability setHostName:@"www.JoshHighland.com"];
 NetworkStatus remoteHostStatus = [reachability remoteHostStatus];

if(remoteHostStatus == NotReachable) {
 //no internet connection
 }
 else if (remoteHostStatus == ReachableViaWiFiNetwork) {
 //wifi connection found
 }
 else if (remoteHostStatus == ReachableViaCarrierDataNetwork) {
 //EDGE or 3G connection found
 }