Current Cisco end-point implementations do not take into consideration Mobile IP (they are not aware of the existence of a Home Address and a Care-of-address that will change as the node moves). Symbol has been working on wireless mobile clients for IP telephony, I am not sure if they have included support for mobile IP on their nodes, as far as I know they haven't.
For starters, the stack handling routines would have to be changed so that the connections are established between the Home addresses and not the care-of-addresses. Plus, I'm sure there are many other factors that add to this equation.
