Over the past 6 months, there's been a rapid acceleration in people telling me about VCC - Voice Call Continuity. This is the emerging standard for SIP-based call handoff from WLAN (or other IP networks) to circuit-switched cellular.
Although it is still at the stage of a "requirements document" from 3GPP, rather than a defined standard yet, it is getting an awful lot of mindshare from vendors and operators. It basically seems to be a way of tying together the various semi-proprietary SIP approaches from BridgePort, OutSmart, Convergin, Stoke, NewStep, Azaire and the myriad other specialist firms offering convergence gateways/servers/switches.
What's not obvious to me (maybe it would be if I waded through the technical documents) is whether VCC is only applicable to dual-mode solutions running in a full operator IMS context - in other words, is it also applicable to non-IMS SIP service providers / users such as Vonage, MSN, Yahoo or enterprise IP-PBX platforms.
Whichever way, it looks like it'll either just be very important... or completely essential.