Sprint Nextel Corp. this week tripled the number of smartphones it offers with a seldom-used technology for tap-and-go payments, as the carrier

and its rivals try to convince a reluctant public to make mobile payments mainstream.

Sprint, which announced at the Consumer Electronics Show that it will add LG Electronics Co.'s Viper and Samsung Electronics Co. Galaxy Nexus to its lineup, is among those betting big on the idea that people will want to use their smartphones as credit cards. So far customers and retailers have remained tepid toward the technology, called near-field communication, or NFC, prompting Sprint and others at the Las Vegas show to try a different tack: touting NFC's "side benefits," which include mobile coupons and digital-key replacement.