Sell what no longer serves you.
eBay just unrolled a new Instant Sell feature that makes it easier to get cash for your old phone without having to worry about any sort of hassle.
Similar to other reseller markets like Gazelle, you'll need to fill in details about your old device. Things like condition, color, carrier, and storage size all play a part in the quote eBay will give you.
If your phone is eligible for Instant Selling, you'll also need to upload a few different images of the device you're getting rid of. Then, you'll get an eBay voucher for the determined value. Print a shipping label, ship off your device, and start browsing eBay for the new goodies you'll get. While this may not exactly be a cash voucher, it's still nice since eBay sells basically everything on the planet.
Currently, Instant Selling eligibility is limited to Unlocked, Verizon, and AT&T phones. Samsung Galaxy S7 to S9+ and iPhone 6s 16GB to iPhone X devices are accepted. T-Mobile, Sprint, and Google Pixel as well as select LG products will be eligible starting in November. If your phone doesn't meet those prerequisites, there's always Gazelle.