Twilio is one of the best startups I've seen or used- they have a brilliantly simple and useful product. You can do a ton with it, it's cheap, and it's all done using dead simple XML.
Look through the rest of their blog- there's a ton of great uses for their service.
(And yes, I know I sound like head of their marketing department- but their product really is that great.)
As head of their marketing department, thanks for all the positive comments. I was pleasantly surprised to find this on Hacker News tonight, I hope it helps some folks set up inexpensive international calling
Some quick math suggests that even billing my time to set this up, it will be cheaper than the piece of freaking garbage service I use to give my family a Chicago number to call that dials Japan for them. I pay them $25 a month (minimum) and the call quality is terrrrrrrrrrrrrible.
Some other features I think would be good to add:
* a pin code, so that no just anyone who calls into the number can use it
* a way to add new people to the calling list from the IVR menu
* a way to check rates and spending from the IVR menu
* a way to gift other people with custom calling cards (a viral feature)
* a web based dashboard of minutes/spend
Look through the rest of their blog- there's a ton of great uses for their service.
(And yes, I know I sound like head of their marketing department- but their product really is that great.)