sorry my last comment got a little dyslexic... shouldn't skype and post at the same time :) minus that does it does part.

I thought about this same feature the other day, the x mph, etc... but I personally saw too many flaws in it that it wouldn't be successful. The comment about bikes and buses is a good example, also what happens when you stop at a light for an excessive period of time, does it does... I'm not sure... This makes sense for the google gps style app thats always in your car, because the only time it's moving is when you're driving... but you mobile phone could be moving for lots of reasons, in lots of various situations (went with a friend in his car - for the activating bluetooth thing)

I would like two features here. Mostly utilize the SMS function of google voice, however the function sbarash mentioned would be great. I actually thought about it today, but I'm not sure if thats easy with the current configuration in google voice to easily swap around ringing phones or not. Though, I'd love to be able to have it ring my house phone when i'm at home and my work phone when i'm at work, rather than google voice current implementation which is based on time of day (and i don't work a 9-5 style job so it's not as applicable).