anyone know an easy way to check the drainage voltage on my cell phone with a multimeter? Only way I see doing this is by selecting random pins and hitting send. Can this screw up my phone?

What I'm trying to get at is to mute my radio automatically when a call comes in???

where would one get diagrams?

and for the nokia express handsfree kit you would have to tap the GREEN lead as the kit doesnt natively come with a mute lead.
I have no idea about LG but just use a multimeter set to resistance mode ..ground the negative contact on the mutlimeter and start poking around while making a call on the pc board of your handsfree kit and when the resistance goes to ZERO then you know you have ground obviously so you can test that out when you hang up and see if its still grounded etc.
alternatively you can set the multimeter to 12v or 3v or whatever DC and test out a lead on the pcb to see which one goes up in voltage during the call and hook that to a relay and use the relay to ground the mute lead on the HU.
Last option..at the risk of sounding lame..who knows maybe the color coding is uniform for some manufacturers.. give the green and yellow leads a try and see what those do???
hope that helps.