My 4S is my daily phone and I use it for development too. When I got my new MacBook Air however, it wasn’t connecting properly. It connected and disconnected rapidly, vibrating each time, iTunes throwing up 50 messages saying the device was no longer available, Xcode the same. This was frustrating, my 2008 Macbook still worked with the 4S, but the new MacBook choked on it.
I bought a load of cables, none of them official Apple cables, none of them worked. They weren’t all cheap either. They’d charge from the power adapter but nothing more. In frustration today, after months of this crap, I decided to pay €20 for an official Apple 30-pin to USB Cable.
It works, flawlessly. Lesson learned Apple.