The president of Sprint’s prepaid business will leave the company in August to take a position at American Express, where he will head up an initiative to expand alternative mobile and online payment services in the company’s new Enterprise Growth Group.

Dan Schulman became president of Sprint’s prepaid group in 2009 after Sprint acquired Virgin Mobile USA, of which Schulman was the founding CEO, for about $800 million.

“When I joined Sprint, we had a great opportunity to change the way prepaid was delivered to customers,” Schulman said in a statement. “I couldn’t be more satisfied with how we have executed against the multi-brand strategy and the strong future prepaid has ahead of it.”

Calling Schulman one of the best executives he’d ever worked with, Sprint CEO Dan Hesse said Schulman left the company’s prepaid brands in “strong shape.”

Schulman will be replaced by Bob Johnson, president of Sprint’s CDMA business, who will assume responsibility for the carrier’s market strategy in the prepaid space while retaining his current CDMA responsibilities. Johnson was named president of Sprint’s CDMA business in May 2009 after serving as COO for Sotto Wireless in Seattle.