voip network hopping

[shawn wilson <ag4ve.us () gmail com>]

i'm curious if there is any spec in the voip protocol suite that
allows one to maintain a call while changing networks?

what i want to do is setup a softphone on an android phone. however,
this won't work very well if i can't switch from wifi -> 3g -> wifi (i
doubt wifi -> wifi is possible because of hardware limitations). my
alternative is to get asterisk to put the call on hold and play an
automated message if a reconnection (and unhold) takes >1 second. i
would expect that ip telephony would allow for some type of hopping
though, i just don't know what to google for?