I've left my phone on in lighties before. You can here the noise as the mobile is "polling" ( at least that's what the Telstra Techs call it ) the network. It can be quite loud sometimes.
I have never seen it effect the Nav instruments whilst this was going on.
I've left in on more times than I should in the 777 too, nothing ever heard on the radios. I guess I'm a bit further from the aerial !!