July 27 (Reuters) - Amazon's Leo has proposed a new constellation of ‌up to 5,105 satellites to ‌provide direct-to-device voice and data connectivity, joining a ​growing race among satellite operators to beam cellular service directly to smartphones. The proposed direct-to-device network would provide voice, ‌messaging, data ⁠and emergency services in areas beyond the reach of terrestrial ⁠cellular networks, with deployment beginning in 2028. The service will partner with ​mobile network ​operators globally and ​use Globalstar's mobile ‌satellite spectrum following Amazon's agreement to acquire Globalstar earlier this year. The move expands Amazon's satellite ambitions beyond broadband internet and intensifies competition in the ‌direct-to-device market, with ​SpaceX, AST SpaceMobile and ​Lynk Global ​also developing satellite-to-phone services. A ‌growing shortage of rocket launch ​capacity ​has, however, become one of the biggest constraints to deploying a ​wave of ‌next generation of satellite constellations.