I have been sitting on a half post for a while now on setting up Asterisk on EC2 and then this past week someone else came out with a post on how to install Asterisk from scratch on EC2. I figured I would wrap up what I have since I take the path of installing Asterisk on VirtualBox first then converting that disk image to an AMI as I outlined a few weeks ago when I got serious about testing out the Asterisk on EC2 concept.
Reading over the comments on the Voxilla post you will see some concern about how cost effective putting Asterisk on EC2 would be. Even if the cost is an issue for normal use I think Asterisk on EC2 could work for bursts of outgoing calls or even temporary conferencing systems. Part of what I wanted to do was find the least resistant path to getting started so I went with Trixbox since it has a lot of tools pre-installed and support for Gizmo5 that was very easy to set up. The key with Gizmo5 is that it is cheap, works with Asterisk via SIP and you can have incoming calls for free from a land line so it is easy to test cheaply.