A year ago, few people in the U.S. had ever heard of BilltoMobile, a direct carrier billing company with roots in Korea. But the San Jose, Calif. company is fast emerging as a leader in the mobile payments space with direct billing arrangements with Verizon and AT&T and Friday, it’s adding Sprint to the list.

The latest announcement extends BilltoMobile’s reach to about 240 million customers in the U.S., who will be able to make purchases and charge them directly to their cell phone bill. BilltoMobile is actively looking at locking up more carriers in North America and is expanding the number of merchants it deals with directly.

via GigaOm.