OK my understanding is that the TFT acts as a hub, connecting BT devices to each other (similar to the way some BT helmets act). You need a device to act as an input device for your phone which the TFT currently doesn't - it could presumably be programmed to do that (like the WunderLINQ) to relay commands from the wonderwheel but I suspect there isn't the demand to do that to make it worth investing the €€€s. It would only be a minority of people who'd want to use a ear phone attached to a phone with a cable as many modern phones don't even have headphone jacks and also to avoid the cable spaghetti. Most people use BT headsets with their phones, and most on bikes would likely go for BT kit attached to their helmets.
EDIT: it's worth noting that Sena at least have solved a similar problem for their comms kit by having a BT remote control which can be attached to the bars and acts as an input device. Perhaps worth seeing if there's something similar for your phone, or even contacting Sena to see if their kit can be used with other BT devices?
