Carrier Installment Program with iPhone 7+

Hi I'm trying to get a iPhone 7, I don't use ATT or T-Mobile since I have a Ultra GSM network SIM Card.
When I pick T-Mobile to get started I can only do one time purchase for the full price.
But when I pick ATT I can choose different program, and I saw 24 month Installment Program.

So my question is, if I purchase my iPhone 7 though the installment program, will I still be able to use it on my Ultra mobile sim card?
Below is the remark on installment program, it sounds like you have to have one of the 4 national carrier in order to activate your phone, but it's already a unlocked phone, can I use my Ultra mobile card to activate it?

"Apple iPhone Installments is available to qualified customers with a credit check and eligible U.S. credit card. Requires a 24-month installment loan with a 0% APR from Citizens Bank, N.A. (subject to any interest, fees, or other costs payable to the issuer of the credit card), and iPhone activation with one of these national carriers: AT&T, Sprint, or Verizon. Activation on T-Mobile available in Apple Retail Stores. Sales tax and any applicable fees due at time of purchase. Full terms apply."

 

anyone?