Margaret,
I know that this isn't how we typically do things in the IETF.
However, I am not sure that we are doing this in the IETF. The only
place I know that this particular problem is being considered is in
the IEEE (802.21, IIRC). It also seems likely to me that some of
the cell phone standards bodies are looking at this (3GPP or 3GPP2,
for instance), but I haven't heard of anything specific going on
there, have you?
I think that mobile IP could be used for something like this, but not
without cooperation from the cell phone providers, right?
Going further off-topic - in 3GPP, interworking is being specified.
MIP and Mobike are being considered for solutions for session continuity;
but then there are technologies like UMA which essentially tunnels the
cellular protocols over WLAN. This Iljitsch would probably consider
serious voodoo, but that is fodder for more off-topic posts.
3GPP2 is already using MIPv4 and has interest in MIPv6 and are studying
how to provide session continuity for CDMA - WLAN handovers; MIP being
a strong potential candidate. My info on this may be somewhat outdated,
though.