The agreement has the two companies agreeing to "multimedia messaging services interoperability," which enables their subscribers to send and receive photos and videos.
VeriSign is handling interoperability for Sprint, based in Overland Park, Kan., through Verisign's hosted and managed service called LightSurf GX-MMS.
Both companies said the agreement expands the number of people their subscribers will be able to reach. The deal, however, could also help the bottom line, since carriers often charge for downloads based on the size of the file.
At the end of last year, T-Mobile USA, based in Bellevue, Wash., had 17.3 million subscribers. Sprint had 24.8 million wireless customers.