I think text to speech is the future, and it's very nearly there. The system used by LUL at King's Cross is okay, but they've got to continue to tweak it, especially when it does long sentences and has the pauses in the wrong place.
It makes much more sense to work to this as a solution as it means you can easily change announcements, or customise them, to suit your needs and not need (sorry Phil etc) to hire a voice artist and re-hire for updates.
The key to successfully pronouncing station names (or even TOC names) is to have a look-up table that will give the system the phonetic data for a name. Therefore it will always be right, something that isn't always the case on a SatNav reading place or road names. Again, this is now happening with modern maps containing this data, if the satnav manufacturer chooses to pay for it.
There are quite a lot of online TTS (text-to-speech) engines around, but here's one that has lots of voices. Unfortunately you can't enter a whole announcement as there's a character limit, but it's a bit of fun (try Damian or Vixen, or ransom to hear mixed voices)
I had mine saying: The train approaching platform one does not stop here. Please stand back from the platform edge.
http://www.voiceforge.com/demo
Incidentally, TTS also makes it possible to do multi-lingual announcements on an ad-hoc basis if necessary.
And another site:
http://text-to-speech.imtranslator.net/
http://tts.imtranslator.net/GqfW - example announcement from Hatfield
http://tts.imtranslator.net/Gqfm - made up running and engineering information (misspelling of WGC is deliberate!)
I can't see how any TOC would (or should) be investing in a system that requires updated voice recordings, editing etc. I am sure Phil Sayer could provide the voice data for one of the TTS companies too, if he hasn't already.