Sprint is in talks to buy the 49 percent stake in wholesale mobile broadband operator Clearwire it does not already own, according to Financial Times sources.

The discussions are apparently at a preliminary stage, but Sprint is exploring the possibility of buying out shareholders including Comcast and Intel, and launching a tender for other outstanding stock.

Securing full ownership of Clearwire would allow Sprint to more effectively challenge rivals Verizon Wireless, AT&T and T-Mobile USA, by bolstering its 4G position.

Sprint is currently subject to a merger with Softbank in which the Japanese operator group plans to buy 70 percent of the US number-three for US$20.1 billion.

Shortly after the Softbank deal was announced Sprint bought a small stake in Clearwire to gain majority equity control over the company. This deal did not give Sprint full control of Clearwire’s spectrum however, which is overseen by a special committee.

The FT said Clearwire’s share price rose 12 percent to US$2.68 on the news, with CNBC reporting that Sprint was in talks with some shareholders to purchase shares for US$3.

Clearwire was formed in 2008 as a joint venture with Google, Intel, Comcast and Time Warner Cable.