For Android phones (.mp3 file):
Follow the instructions for METHOD 1 here: http://www.wikihow.com/Add-Ringtones-to-an-Android-Phone
For iPhones (.m4r file):
Open the .m4r audio file in iTunes. It will appear in the Tones (aka ringtones) tab. It's the one with the bell icon. If you want to rename it something other than your email address, do so now in iTunes.
Connect your phone to iTunes.
Drag the Tone from iTunes onto your phone.
To set a Tone on your iPhone:
a. Go to Settings > Sounds > Ringtone
b. Select the Ringtone. It should be at the top of the list and will be your email address unless you renamed it earlier.