My current phone is a Sprint Palm Centro - upgraded from a (very old) Samsung A400. Love it! I've been using PalmOS devices since the Palm Vx and chose the Centro for software compatibility, extensive software selection and the fact that it just works.

Audioengines website indicates that you can use a USB battery pack to power the devices -- I've bought a couple of these from PocketPCTech and BoxWave to power my Palms. :)