a lot of parents who decide what phones their teenage kids can have.
LOL. I have a fair amount of experience, both in software and hardware. Think about it for a minute - the purpose of an antenna is to collect signal. When you bridge the antennas, the issue is NOT that signal from the wifi/bluetooth is being sent to the 3g antenna. The issue is you have changed the effective size of the 3g antenna. It no longer functions properly as an antenna. Therefore the signal-to-noise ratio of what the antenna can send on to the circuitry drops substantially - there is nothing there for the signal processor to work with.
How many parents are buying their teenagers iPhones?