Apple’s iPhone 7 and 7 Plus remain on backorder for certain models. With that being said, you can now purchase a SIM-free iPhone, meaning that it is totally carrier-unlocked in the US and will work with any carrier, including support for Sprint and Verizon’s CDMA networks, as well as GSM network connectivity.
The iPhone 7 has shorter wait times than the iPhone 7 Plus, and if you want the Jet Black iPhone 7 Plus, as a SIM-free model, you’ll have to wait 6 to 8 weeks for it to ship. By contrast, the iPhone 7 in Jet Black is taking 3-5 weeks to ship.
Unfortunately, it looks like you still have to choose a carrier when purchasing the phone through Apple’s iPhone Upgrade program; so you can’t buy a SIM-free iPhone on the iPhone Upgrade program. Still, you can apply for Apple’s 18-month promotional financing via a Barclay Visa credit card. It will let you pay the phone off in installments, but won’t let you upgrade every year.