How To Use Rhythmbox To Transfer Music To Any Mass Storage Device (Phone, USB Memory Stick) [Sync]

Rhythmbox is simply great for transferring music to your iPhone or mp3 player. It automatically converts the tracks and all that.
But what if you want to use Rhythmbox to transfer music to your phone which is detected as a mass storage device? Or an USB memory stick? Well, you can't do that - not by default.