I agree patient line is a complete rip off but I think you'll be surprised to know that they are actually using VOIP.

They use their own GUI to the standard windows H323 client linked back to a Cisco unit.

There is another company that make these too called Hospicom and they are a bit cheaper.

I also believe Patient line are currently under investigation.

These companies give the NHS the whole unit for free (games, TV and Phone) for free and operate completely on the profit from their charges