I'll add in a couple of my own thoughts about this:
a) Microsoft (NASDAQ:MSFT) seems completely and utterly disinterested in IMS. Yes, I'm sure there someone selling to carriers who is pitching LCS as a SIP app server, but in terms of an end-to-end story, this is all about turning voice and messaging into "another feature" in the general corporate IT domain. Certainly whenever I've asked about IMS-capable phones, I've got blank looks or "Oh, you mean SIP? Windows Mobile's got that already."
b) Alec's post should be required reading for "mobile PBX" and centrex enthusiasts. About twice a week I have to counter the argument that all enterprises will just ditch their PBX-based phones (plastic or WiFi) and switches, and just start using mobiles with telephony as a "service." Normally I talk about higher-end IP-PBXs becoming part of corporations' IT infrastructure, and the fact that many companies like to retain control of their own voice systems for a variety of reasons. Migration stories are also important here - even if companies do want to be "all mobile," cellular operators aren't going to assist a huge two-year migration towards that goal as they usually lack the integration and consulting expertise. I've also recently started talking about Asterisk and other server-based platforms dragging corporate voice even further away from network-based mobility solutions, but I hadn't really recognized the depth of movement towards embedding PBX capability in low-end boxes.
The argument that "SMEs will just buy a femtocell / WiFi router and use a hosted mobile PBX solution from the carrier, linked to mobile phones for the employees" starts to carry much less weight when you consider that the femtocell / WiFi router might just have a PBX built into it for peanuts.
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