Sprint Nextel CEO Dan Hesse warned Wednesday that carriers will need to convince subscribers to spend more on existing services rather than count on attracting lucrative new customers to keep revenues growing. After reporting earnings, Hesse said, "the economic model will change. And postpaid phone service will not be as dominant in terms of what drives success in the market." Separately, Sprint said it will begin rolling out its HD Voice service over Long-Term Evolution networks in several markets this quarter, after resolving service-quality problems. The carrier said HD Voice would be limited at first, and it could take several months before interoperability issues are resolved.