Here's something which I have never seen before and which makes a lot of sense.
By combining VoIP and IM the device helps to define the concept of presence. Hopefully, I'll be able to check one out soon and provide the details.
Imagine getting a call on your cellphone that originates over MSN or Yahoo messenger, without having to go over a carrier until it reaches you.
The big question remains the QoS on the IP side of the call. That, and the usual cell phone drop outs and bad cell sites aside.