With WAVE (Wide Area Virtual Environment) it is possible to interconnect all kinds of different voice equipment (voip, GSM, UHF etc.) using an IP middle layer and a channel (like IRC-chat) approach.
WAVE is brought to market by www.twistpair.com
It would be great for SKYPE to bring that kind of technology to the consumer (not SME and larger business) level.

I am contemplating of combining a UMTS-pcmcia card with SKYPE to see what the quality is, so I can have a www.Xybernaut.com MATC wearable enabling me to make international phonecalls for remote maintenance.