T-Mobile US is looking to buy wireless airwaves from larger rival Verizon Wireless to bolster its mobile network capacity for data services, a source familiar with the matter said on Tuesday. While T-Mobile has approached Verizon about buying the spectrum, the process is still in the early stages, according to the source, who asked not to be named. The source was not authorized to discuss the matter. T-Mobile, the No. 4 U.S. mobile service provider, might have to pay as much as $3 billion for the airwaves, which are not being used by Verizon, according to one analyst estimate. The airwaves would give T-Mobile additional network capacity to help it catch up with its bigger rivals in delivering high-speed wireless services. T-Mobile declined to comment on Tuesday. Representatives for Verizon Wireless, which is owned by Verizon Communications Inc and Vodafone Group Plc, were not immediately available for comment.