Google has speech recognition services available for use from mobile phones (Android has it built in, iPhone users can use the Google application) - http://www.google.com/mo
I read this presentation few weeks ago- http://www.abelski.com/courses/android/speechinput.pdf
The following link is a 3 mile high review of the Google Voice Server ....
http://www.google.co.jp/events/developerday/2010/tokyo/pdf/tt1-gruenstein.pdf