When is an IPTV service not an IPTV service? A good question. informitv.com claims that the 150,000 customers with BT Vision do not count and ignores the various video sites such as YouTube or catch-up services like BBC iPlayer and Channel4 4oD.
The crown apparently belongs to Freewire TV who multicast the main 25 Freeview channels over an IP network to student halls and residences and currently have some 40,000 people on the service. The service is free, with top-up deals available to allow you to view channels such as Setanta sports. Currently it is limited to running on Windows XP or later, with a TV set-top box and Mac support in the pipeline.
So if your definition of IPTV is that it must use multicast to deliver the TV channels then FreeWire wins. BT Vision only broadcasts the Video-on-Demand material over the broadband connection preferring to receive the Freeview channels over-the-air so it is a hybrid model rather than an IP based one. If your definition of IPTV is any video service over a broadband connection (using the Internet Protocol, or "IP"), then the various catch-up TV services (iPlayer, etc.) and video websites such as YouTube come into the reckoning. One key advantage of the BT Vision and many online video sites is the ability to pause content, something that appears not to be in the pipeline for the Freewire service. It is to be noted however that multicast is likely to play an increasingly larger part on broadcast distribution via the Internet.
While the service is currently only available to students, there are suggestions that Inuk's wider rollout of IPTV services maybe on the cards.