I'm at an IMS conference in Geneva at the moment, and it's helped me crystallise various separate bits-and-pieces I've observed into a coherent theme.
The next "big thing" for mobile operators is..... offering own-brand VoIP services over fixed broadband.
The logic goes something like this: all our best customers are getting ADSL or cable at home. This is inevitable; broadband using fixed-3G is a tiny niche. At some point, they will start to use their fixed broadband for VoIP - maybe bundled from the ISP or telco if they're aggressive about transitioning from PSTN, or else Skype or other Internet-based VoIP. This is, again, inevitable. Given that they're getting VoIP anyway, why not an operator-branded and -billed service?
There are variations on this theme as well - maybe offering VoIP-enabled USB sticks so travellers can use them in Internet cafes, for example, hooking into their usual operator services like SMS via a PC.
And, of course, offering fixed VoIP gives mobile operators a reasonable application to use as economic justification for an IMS deployment. Given that there won't be mobile IMS-capable handsets available in volume for several years, it makes sense to target other IMS-capable endpoints like PCs. And fixed broadband gets around the thorny issue of indoor 3G coverage that would otherwise limit the usefulness of real-time or multimedia mobile IMS applications.
Certainly, there's considerable vendor push already. I saw a Siemens presentation yesterday that specifically focused on this issue, and Nokia has this morning announced something similar in its Communication Suite offering.
So for example, it seems probable that both O2 and Vodafone will leverage their broadband partners/acquisitions to offer VoIP. The Skype/3 deal is obviously a different approach to the same opportunity.
Also, long term, this sets the scene for true mobile VoIP, which will happen eventually. It should be easier (and more valuable) to link existing fixed VoIP customers with wireless VoIP at that point. Gaining a foothold is essential, as otherwise the whole VoIP world will be even more dominated by the fixed/broadband/Internet/enterprise providers.