iPhone is locked for shared Bluetooth connections. Between iPhones it's easy using GameKit. Between the iPhone and the headset also, as I understand it, is easy. But when it comes to talking with an arbitrary device via BT, you need to use the structure of an external accessory. It's great and easy to use, but you need to connect to a licensed Apple device. For the project that I was working on, it was great because we control the BT device we are connecting to. But in other cases, this restriction can be serious negative.