I'd say whilst flying VFR the risk is so minimal as to be non-existent. No-one seems to have been able to demonstrate any sort of interference, but even if there was some small effect then it shouldn't endanger a VFR flight. As someone else said, you hold your heading by looking outside.
I've found the practical altitude limit to be about 2,500 ft. But I'm sure it depends on the network, the model of phone and the location. So if any LARS unit wonders why someone reports descending 2,500 ft and then 2 mins later reports climbing back up then it was probably to get a text sent! :-)
The "tick, tick, tick" you hear when the phone is transmitting is not interference with the radio, it is the effect the phone has on the loudspeakers in your headset. You'll hear exactly the same thing if you place a phone which is 'doing something' near any other 'live' loudspeaker such as a small kitchen radio, a hi-fi, or indeed in the car. The ticking isn't a problem, it's just annoying.