That would be an interesting experiment - fully unregulated airwaves. Imagine AT&T jamming Verizon's 3G signal, private transmitter hijacking terminals, etc.
Well, in the jamming case, Verizon would probably jam AT&T back. So neither is getting any revenue, and they are left to work out a truce or face bankruptcy.
There exists swathes of practically unlicensed spectrum, such as ham radio and 2.4GHz. While regulation exists, large scale enforcement is pretty much unheard of, yet it works pretty well.
The big cellular telecom standards (GSM and CDMA) assume a very orderly environment (contrasting the 801.11x standards that are more adaptive), so they would probably look different in a world with unregulated airwaves.
EDITED to add: For the purpose of such a thought experiment, It's not practical to imagine what would happen if the current GSM 2G and 3G spectrum just became unlicensed overnight. There is a huge infrastructure investment, both on the carrier and consumer ends that would become worthless, and this is clearly undesirable. Rather, imagine a block of airwaves (say, ex-military or analogue broadcast TV) being released with zero or minimal regulation (no exclusivity, basically).
