We install a lot of sip based handsets. Mostly Polycom because they seem the most "sip compliant" and the price point is OK compared to the more proprietary SIP handsets. When Polycom introduced the vvx500 model a few weeks back, they alluded to be able to dock a smartphone, and extend your desktop onto the vvx's touchscreen (scroll that mouse a little further, though you might need a mousepad upgrade).
The details were sparse, and noone has seen them in warehouses, meaning the product is not shipping when they said it would. That's OK. It distrubed us that it had some central features that were platfrom specific to the Microsoft Exchange messaging platform.
What I am waiting for is for a hardware vendor to pickup where Android 4.0 is leading us. It has a sip stack built into the OS. At some point the desktop handset COULD be the smartphone you carry around, and simply docks/charges and drives a bigger screen if desired. Other pre 4.0 android devices do this now (Atrix, Bionic). When it is docked it could invoke applications (turn 3g/4g off and forward your cell calls to the office number, and reverting that when not docked) , and use an embedded Ethernet in the dock itself. So the dock has an associated application. It might also have a standard handset/headset, keypad like any other phone. My wife's phone does this a lot of this with her Bluetooth enabled minivan.
I don't think it's imminent, but when Android 4.0 get polished and the sip stack matures a bit, you could easily have a contender for the desktop phone replacement in the SIP world. At the same time, I don't see why a hardware manufacturer doesn't start making a replacement desktop only phone for SIP using Android. We think it's up to it. It would be awesome handy for firms using Google Apps and have a sip infrastructure in place already. Clearly it could handle the Video (h.263/h.264) if the hardware specs were worthy too.
Panasonic introduces 7" android handset.
Now when the sip stack becomes more embedded into the OS to handle more functionaity (NAT/ICE/TURN, etc.) or also offers a VPN client... clearly this is going to go somewhere.