Consumers traded in a record number of smartphones during the kickoff of the 2017 holiday shopping season, according to a new analysis from retail services company Phobio.

The report found that smartphone trade-in volumes increased by 57 percent on Black Friday and 30 percent on Cyber Monday compared to the same days in 2016.

Phobio officials attributed the increase to a strong secondary smartphone market worldwide — which bolstered prices for consumers looking to trade in their phones.

This year’s shopping season also followed promotional campaigns, which highlighted trade-in values, for the iPhone 8 and iPhone X. Verizon touted up to $300 in savings on iPhones with select trade-ins, while AT&T offered a $200 credit for customers that traded in smartphones and purchased a smartphone on AT&T Next. Sprint detailed $350 in savings for either trade-ins or bringing phone numbers from another carrier.

The average trade-in value of smartphones, the analysis added, rose nearly 60 percent for working-grade devices and 81 percent for damaged-grade devices between 2012 and 2017.

“Mobile operators and retailers are leveraging trade-ins as a mechanism to upgrade customers to the latest technology, at a lower price, getting customers back into contact this holiday season,” Phobio CEO Stephen Wakeling said in a statement. “With the shopping season in full swing, we anticipate strong market for trade-ins throughout December, which represents a win for carriers, retailers and consumers.”