Apparently yes
"Copied from a post on Tmonews"
This is info from a T-Mobile 'Online Chat Specialist':
GeraldC: I have checked your account and I can see that yes, you do have the JUMP feature on the account! Pre-orders for iPhone 6 and iPhone 6 Plus will begin worldwide at 12:01am Pacific Daylight Time on September 12.GeraldC: Also, A pre-order device can be used for a JUMP! redemption if you are eligible at the time of the pre-order.You: So I can go online tomorrow and utilize the JUMP! redemption to pre-order?GeraldC: Definitely!