What is the best way to buy an unlocked iPhone 7?

Hello everyone,

I am currently using T-Mobile and want to get the new iPhone 7. Since there is no option for a sim-free iPhone, what is the best way to buy the new iPhone? Should I get the T-Mobile one at full price? I know that it will be unlocked version but it will come with a T-Mobile sim so what will I do with the sim? Put it away or give it to T-Mobile? Or should I wait for the sim-free version to be released, which I don't think will be out until November and I don't want to wait that long.

Thank you all in advance.