I may have re-invented the wheel: Tossable Digits uses the same extension-based scheme I proposed. They’ve got a different business model than I had in mind, they have a different security model than I had in mind, and they don’t seem to have some of the other usage-tracking features I’ve been thinking about — but on the other hand, they have a commercial service you can sign up for today, and all I have are doodles and a demo.

I wish them success, and if you want to use Disposable Phone Numbers immediately, they’re the place to go. If you end up using their service, feel free to comment here and let us all know how well it works.