Boost Ready To Build On Big Quarter

"We're very bullish and very pleased with what we've seen on Boost Unlimited," Sprint CEO Dan Hesse told analysts Monday.

That surge in popularity wasn't painless, however, as Boost users experienced long delays in receiving text messages in the first couple of months and vented their frustration at dealers. Carter said the problems were with the platform used to process texts on the network, not the network being unable to handle the additional call volume, and those problems have been fixed.

"Right now the system is definitely where it needs to be and will stay there going forward," he said.

He added that the company is also getting a better handle on its handset inventory after some stores experienced brief shortages shortly after the $50 offer started.

Keeping those new customers happy will be key for the Boost Unlimited offer to have a long-term benefit for Sprint. Prepaid customers can switch providers relatively quickly because of the lack of contracts and their financial history sometimes makes them risky as customers.

"We think the prepaid market may be one of the best sources for future growth," Dave Novosel, an analyst for the Gimme Credit corporate bond research firm, said in a note to clients. "The question is whether or not Sprint can do it profitably, as credit quality for prepaid users is typically lower."