Well, the issue is even having the phone on since your phone needs to been in communication to cell sites via the control channel (which determines how to send

Well, the issue is even having the phone on since your phone needs to been in communication to cell sites via the control channel (which determines how to send an incoming call to you, what tower you should be using, and allows for sending/receipt of text messages). So, you might not be causing problems for the traffic channel and the speed issue probably wouldn't be a problem, but you'd still be causing problems on the control channel even by having the phone on. Granted, if a few people did it, it might not matter, but if everyone did you'd have the exact same problem where you'd be defeating frequency re-use.