I've written an app that allows you to set the ringtone .. on someone else's phone.
I'm looking for people to help test it across a variety of android devices. Most seem to work just fine.. but there are the occasional ones that just don't play ball.
You can also record a ringtone and send that ... and when you ring your friend next, that'll play !! (You can switch off automatic downloading and installing too).
The app is called "tonepush". You can read about it, watch a video of it etc here: TonePush
or get it straight from the market here: https://play.google.com/store/apps/details?id=com.tonepush.android