I have a wireless headset for my office phone (a Plantronics Savi 700 series) that connects to my office phone (via USB or standard phone headset cable) and also connects via Bluetooth to my cell phone, and switches seamlessly between the two. It supports three simultaneous connections: via USB to a PC softphone, via Bluetooth to a mobile, and via headset cable to a standard phone.
It's very nice.
I think my specific model is the W740.
http://www.plantronics.com/us/produc...uId=sku5800019