UMA

Unlicensed Mobile Access is trying to be a relevant approach to providing mobile-like voice services on top of Wi-Fi.

• UMA Technology

The pretty diagram everyone takes for granted, and which makes it look simple:

The one with the real juice, where you can see there are quite a few things to figure out (namely the Wm and Up interfaces, which are what needs to be properly standartized):

Notes:

Technical specs are here.

• The Stage 1 specs are user-level (i.e., useless) documents.
• The Stage 2 specs are mostly a feature shopping-list (and comparison between UMA requirements and existing features in GSM/GPRS)
• The Stage 3 specs have the most meat on them, but still lack a lot of detail and interoperability specifics