Have you ever heard the controversial theory that prolonged phone use might cause cancer?
In case you're worried about that, and electromagnetic waves and volume, Sanity for your Android phone is a pretty effective way to cut back on your exposure to these things.
Sanity is a software program that automatically turns off Wi-Fi and Bluetooth signals when you're talking into your phone. What's great about this is that you can go through a "Devices to Disable" listing to specify which of your phone's devices you'd rather not have silently humming into your ear while you're on the phone. In case you happen to be having a conversation on a Bluetooth device, and don't want to shut off your Bluetooth, you can click on the "Skip If Headsets Are Used" option so you don't end up disconnecting your call.
Perhaps this app's coolest feature (and, I think, most useful) is its proximity sensor, which can be activated to turn on or off, based on how close your phone is to your ear. If you move your phone away from your head while Sanity is on this setting, it will automatically turn on your speaker phone. What I like about this option is that it, obviously, makes going hands-free a much quicker process. If you're in a moving car, this is a much quicker alternative to dangerously fumbling for buttons, trying to get on speaker phone. (It also keeps you within the limits of cell-phone law.)
Because different people come through your receiver at different volumes (my mom's normal, indoor voice can be classified as shouting, and my dad's phone settings, which he has no idea how to adjust, make him sound like he's whispering), you can use Sanity as a sort of shortcut to getting the right adjustment for a comfortable listening volume.
Because achieving perfection always takes practice, I suggest you play with this one a little bit before you hop into the car. Because it's fairly intuitive and self-explanatory in setting up, I don't think many will have trouble figuring out Sanity.
This app is free, but because it's kind of a lifesaver, you might want to consider handing over a few bucks to the developers.