If you are signing up with Metro PCS, I am unfortunately informing you that you cannot get the Samsung Galaxy s6 or s7 with a payment plan. Metro PCS only offers these phones to be bought outright.
If you are interested in purchasing either of these phones on a payment plan you may want to consider another carrier.
Click here to Compare Samsung Galaxy s6 Plans
Click here to Compare Samsung Galaxy s7 Plans
There are many different phone payment types and many different carriers who offer these types of services.
Remember choosing different ways to pay such as through monthly installments, early upgrade or lease will make that hefty upfront cost evenly divided into a 24 month payment period.