[Hugsun]

My impression was that you could send SMS through iMessage but when it's between iphones it doesn't use old school phone tech at all and just goes through the internet like other web based messaging apps. But only between apple devices of course.

[hedora]

Yes. It auto upgrades to a decent protocol when you are sending to an apple device. You can associate any combination of phone numbers and email addresses with it, so you don’t need a phone number to send iMessage messages.