Jim had this today... Very interesting. It would be a cool to do VoIP from your Symbian handset, for example...
This is something I've been musing about for a while, but not something that I really expected to be built yet, IXI mobile have built a personal mobile gateway that operates as a gateway or router between GSM/GPRS and Bluetooth (or 802.11, 802.15) and also as a micro server and app server.
Using one of these with a lightweight Bluetooth headset and/or pda is an interesting prospect, imagine the possibilities of having one of these boxes in your pocket, briefcase, or even leaving one in your car glovebox for ad-hoc usage. If you think mobile phones are small now, just wait until GSM/GPRS wireless functionality migrates into a box like this, power requirements for the handset will drop by a factor of ten or more, meaning wafer-thin, flexible, or even roll-up "phones" will become the norm, maybe the keypad, display, and headset will seperate further into components.