Telecom investors didn’t wait for the details. AT&T stock fell 7.3% in postmarket trading Thursday, while T-Mobile and Verizon both dropped 6.6% as of 5 p.m. ET. SpaceX rose 1.5%. The trigger: SpaceX bought low-band spectrum, the airwaves that carry calls and data, which can reach phones indoors. It still needs approval from the Federal Communications Commission, and the price wasn’t disclosed.