Here are iOS Objective-C headers as derived from runtime introspection.

The headers were generated using RuntimeBrowser for iPhone.

You can use the headers this way:

NSBundle *b = [NSBundle bundleWithPath:@"/System/Library/PrivateFrameworks/GAIA.framework"];
BOOL success = [b load];

Class SKTelephonyController = NSClassFromString(@"SKTelephonyController");
id tc = [SKTelephonyController sharedInstance];

NSLog(@"-- myPhoneNumber: %@", [tc myPhoneNumber]);
NSLog(@"-- imei: %@", [tc imei]);

Note that many other unique identifiers can be retrieved:

Class AADeviceInfo = NSClassFromString(@"AADeviceInfo");
NSLog(@"-- serialNumber: %@", [AADeviceInfo serialNumber]);
NSLog(@"-- udid: %@", [AADeviceInfo udid]);
NSLog(@"-- appleIDClientIdentifier: %@", [AADeviceInfo appleIDClientIdentifier]);

id deviceInfo = [[[AADeviceInfo alloc] init] autorelease];
NSLog(@"-- wifiMacAddress: %@", [deviceInfo wifiMacAddress]);

You can search the headers with github search:

https://github.com/search?type=Code&q=repo:nst/iOS-Runtime-Headers+radar