Ever since I got PocketTunes for my Treo 600 a couple of years ago, I've been streaming net radio stations or listening to podcasts when I go to sleep, but I've always had to use a couple of cables to charge my phone and hook it up to my speakers, and they've had a tendency to get lost behind my bed or put too much tension on the headset connector. This device solves those problems nicely.
I expect I'll find a few other uses too. It should also work as an improved speakerphone, and I can also make it into a weather-providing alarm clock using the program TreoAlarm. I can even stream my own personal music collection to the phone using GlooNet, although it seems a little silly to send stuff out to the 'net, into Sprint's network, then over-the-air to my phone when local WiFi should work as well.