[LoneSnark]

Depends how you do it. If you use the technique shown here or elsewhere that isolate any power sources away from where you are cutting and splicing then there is no way to cause damage. running a video or audio signal to ground or each other should not cause any damage.

But if are using another technique that allows for the possibility of running power (+5V) to another wire, say video, audio, or even ground, which could cause damage to either the phone or power supply.