As TC points out, one of the biggest unknowns is how they are going to handle the bandwidth demands - and suitable reimbursement for the carriers - how that will be priced/packaged to keep from pinching the end consumers too painfully.
"And we shouldn’t have to wait a year or more for the device, the goal is Q1, according to the report. This indicated just a small slip from the Fall 2009 launch that we had initially been hearing."
[ Though on reflection, the whole customize-your-own-cpu is probably throwing in some of its own monkey wrenches. ]