This DIY Star Trek Bluetooth Communicator, instantly reminded me of a my Star Trek fantasy. Bluetooth is the ruin of Star Trek. But this is a fun quick-n-dirty project.
Basically you're cramming a Bluetooth module and a micro-controller into a toy Communicator and then pairing everything with your phone. As long as you've got voice-dialling, you can leave your phone out of sight and be the snazziest Trekkie on the streets. Just don't come crying to me if someone stuffs you into a locker, rubbish bin or wormhole. [Make]