iPhone FM transmitter - Design The Macally BTCUP for iPhone is a full-channel FM transmitter with a clever design that lets consumers enjoy their iPhone in the car. Fitting into standard car cup holders, the BTCUP keeps the iPhone upright while also giving the driver full access to the touch screen. Its FM transmitter capabilities lets everyone in the car enjoy the music on the iPhone via the car's speaker system. The BTCUP can sync with the iPhone's integrated Bluetooth technology for hands-free usage while driving - something that is increasingly being made law across the United States. As a result, the BTCUP is easy to use for both playing music and managing incoming calls from the iPhone. When a call comes in, auto-switching between music and phone modes allows users to answer the call hands-free for improved safety, then returns to music play mode when the call is completed.