Apple could have cleared up the confusion simply by listing the model number with each carrier option. I'm on Selectel, a Verizon prepaid MVNO.
If I choose Verizon in the Apple Store app, I have to have a Verizon account or set up to order the phone. Is the contract-free T-Mobile offering the same phone. Who knows for sure? There are hints that it may be circulating around, but if you choose it you are notified that it is a GSM phone, while I need a CDMA.
Those who use GSM MVNO's should be fine with the T-Mobile contract-free phone. To make sure I get a phone that works with Selectel, I ordered the Verizon phone reserved to be picked up at an Apple Store 40 minutes away. I'll have 2-3 hours invested to get a phone that should have been delivered to my house on the 25th. While I wouldn't be surprised that Verizon is the reason for the online preorder aggravation in order to get more accounts, it just ought not to be.