BARCELONA, June 29 (Reuters) - Billionaire entrepreneur Elon Musk said on Tuesday that his satellite internet service Starlink was growing quickly and he expected the number of customers to reach half a million over the next 12 months. Starlink now has more than 1,500 satellites aloft and is operating in about a dozen countries, adding more every month, the Tesla Inc CEO said in a video interview aired by the Mobile World Congress, a telecoms industry conference. Starlink, an array of low-orbit satellites offering high-speed connectivity for people living in remote areas, is already offering a trial service and says it aims for near-global coverage of the populated world this year. (Reporting by Supantha Mukherjee and Clara-Laeila Laudette, Writing by Douglas Busvine Editing by Gareth Jones) Our Standards: The Thomson Reuters Trust Principles.