Used cellphones are available from GameStop and Amazon.com. Used cell phones are often considerably cheaper than new ones and many of these phones come unlocked, allowing them to be used on any network.
When buying from GameStop, you can save about $100 by buying a used iPhone 6 as opposed to a new one from Verizon. GameStop also allows customers to trade in an old cellphone and apply the credit toward the cost of their purchase.
Amazon.com has a very wide selection of used cellphones and a robust search filter which allows customers to compare phones by rating, price, brand, operating system, size and many other options.