Breaking contract and porting number for a preorder

Wife and I are on a family plan with AT&T, but will be breaking contract to switch to Verizon on the iPhone 6 launch day. From searching I know I should just preorder a pair of new Verizon phones, then when I port the number my AT&T contracts will end and the ETFs will be applied.

However, with a preorder, when will our numbers actually be ported? At time of preorder, or time of phone activation once we receive the new iPhones? My concern is that if the porting (and thus the termination of the AT&T contract) happens at the time of the preorder, we would then have no cell service between the time we preorder and the time we receive the new phones.

 

Thanks, that's what I figured but just wanted to make sure.