Fret not, however, all you need to do is get the T-Mobile version at full price, and it will come with the Un-carrier SIM but unlocked for use on any carrier, including Verizon or Sprint. You see, the T-Mobile option is the A1984 model which supports all US carrier frequencies, the CDMA standard, as well as T-Mobile's new 600MHz spectrum.
Here's what you need to do:
1. On Apple's 'Buy iPhone page, continue to the model options
3. Choose a color and storage capacity option
4. On the next page, pick the 'Pay in full' option
5. Before payment, you will see the "Unlocked iPhone with T-Mobile SIM" description, this is the A1984 US carrier-compatible model that you will get in the mail.