I wrote recently about VCC emerging as the key SIP-based approach to fixed-mobile convergence. I'll reiterate that even more strongly now. I've just spent two days at the FMC Summit which is still ongoing in Amsterdam, and it has come up over and over again - not just from vendors, but from some of the largest operators in Europe.
Not only are they pushing for it to be standardised ASAP, but they're giving the distinct impression that standardisation is the only thing standing in the way of ditching UMA in favour of SIP.
Three of the conversations I had essentially said the same thing "We're doing UMA in 2006 as it's standardised already, but want to go to VCC in 2007 if we can".
This fits with my understanding that low-level UMA deployment is pretty cheap. It has severe limitations, but it works OK as essentially an extended trial technology - enabling the carrier to get some detail and experience about customers' preferences and key operational practices (billing, marketing, bundling, user interface, pricing, coverage etc). It's also got some handsets already shipping.
Conversely, VCC/SIP fits better with operators' medium-term strategies around integrating quad-play services, many of which won't use a mobile core network, unlike UMA's Voice & GPRS. I'm being told that these services will integrate a dual-mode handset (or even a WiFi-only one) with IPTV, Internet services, gaming, and a whole slew of hybrids.
Interestingly, some carriers are leapfrogging UMA and going straight to a pre-standard SIP version with (again) a VCC roadmap.
My only concern is that none of the handset manufacturers have yet nailed their VCC colours to the mast. To be fair, it isn't standardised yet. And there are some handset software suppliers already advocating it (the MobileIgnite alliance members, for example). However - if there's anyone out their in handset-land that's relaxing after getting their UMA platform sorted, I'd suggest knuckling down and getting VCC on the roadmap ASAP. The same goes for chipset suppliers and SIP software client specialists.