Skype now offers an ATA for $59.99 that includes unlimited calling to U.S. and Canada for a year. I don't think you get a number for that price, so you would only get to make calls, not receive them.
Probably they will sell you call-in service with a number as they do for Skype-over-computer.
I'm using Skype for outgoing calls and it's approximately $60 per year for 10,000 minutes per month. This also does not include an incoming number so I would expect the ATA to remain the same, at least until MS completes the purchase.
