How can I connect multiple wireless headphones to the same iPhone at the same time?
There is another "workaround" that DOESN'T involve Bluetooth. I often train multiple students students for 5K's, 10K's, etc. Since I train multiple students at a time and often use 1-hr long DJ mixes to set paces for everyone, I connect my iPhone to an FM broadcast device (usually limited from a 30-100 feet range). I additionally, I encourage trainees to use wireless devices such as nano shuffles, etc. that can pick up radio FM frequencies. There's no pesky Bluetooth "pairing" compatibility issues and anybody can join in by simply tuning in to my FM frequency; even those with nothing more than a simple portable radio/MP3 player. Although these devices were originally intended for tuning into your car radio, I've found they work just as well as for other mobile devices that can receive radio FM frequencies. They're not that expensive, either.

Link