We had a chance to play around on an Amazon Elastic Compute Cloud so we checked out a copy of FreeSWITCH then compiled and ran a conference on it. And it WORKED!
This came from the FreeSWITCH project, which is a group taking a new approach to designing a telephony (scan back a year and you can find a write up I did on them, they are approaching design in a more Apache like manner then in a way similar to Asterisk).
EC2 running a telephony switch is a clever idea. If your interactive voice response system, IVR, becomes slammed you just grab more computing power from EC2 to handle the call streams. If you could back this with an ability to have your line capacity fluctuate as needed, for PSTN calls, you could handle a chunk of the problems companies run into when they get slammed by calls.
Pretty nifty stuff.