Only days after securing full control of Clearwire and its huge amount of spectrum assets, Sprint has unveiled a guarantee of unlimited data, calling and texting for its customers – while on the operator’s network – “for the life of the line of service”.

Sprint, now run by Japan’s SoftBank, already offers unlimited data services for a flat monthly fee. Concerns about capacity constraints, however, have led analysts to question whether Sprint would eventually have to follow rivals and charge according to data usage.

With the launch of “The Sprint Unlimited Guarantee”, the third-largest mobile operator in the US hopes to reassure customers it won’t be changing its data-pricing course.

Chief executive Dan Hesse, speaking to Reuters, said worries about unlimited services being pulled was a big factor in holding customers back on other networks from switching to Sprint.

“Our research has shown that is a big issue for us in attracting AT&T and Verizon customers,” he said, adding that the guarantee “clearly differentiates” Sprint from its bigger rivals.

And without Clearwire’s airwaves, added Hesse, Sprint “would have run out of gas” on capacity in a few years’ time.

‘The Unlimited, My Way’ plan, which costs $50 per month (for one line) for unlimited talk and text, plus $30 per month for unlimited data on smartphones, is – according to Sprint – $20 per month cheaper versus Verizon’s comparable plan with only 2GB of data.

It is an aggressive pricing move by Sprint, and one, say analysts, that reflects the favoured approach of Masayoshi Son, SoftBank’s chief executive, which rattled bigger rivals in Japan with similar tactics.

“The excitement for investors and consumers is that Sprint now has the spectrum assets, the money to build its network and a leader that has the courage to do it,” Walter Piecyk, a BTIG analyst, told Reuters. “Whether they can execute on that remains to be seen.”

In another sign that competition in the US mobile market is heating up, John Legere, boss of fourth-player T-Mobile US, this week announced that customers could upgrade their phones every six months. Legere also took a swipe at Sprint’s LTE network progress, a move that is likely to set up a heated battle between the two operators as they attempt to claw back market share from Verizon and AT&T.