I spoke to a friend who works at a dealership in Richmond, VA and he said that he wasn't certain if it would be possible to add Sync to an 07, but he does THINK that it would be possible. As far as cost he said that there is no way to ballpark it since they have not actually seen a vehicle outfitted with the system. He said that it could end up being a comparable cost to adding it on to an 08 or it might be very very expensive.
Also, he told me that once the 08 Taurus is released (the first of the Sync models to be released) the dealerships should be able to give an estimate as to how much it would cost to retro-fit the system to an 07 model, because they will have access to the system and will know how much work will be required.
I am in the market for an Edge right now and really want Sync, but I also don't want to wait until Fall to get one.
Decisions decisions.