Apple Inc.’s effort to build its own modem technology will set the stage for a range of new devices, starting with slimmer iPhones and potentially leading to cellular-connected Macs and headsets.The new products will be made possible by an in-house modem chip slated to debut next year, people familiar with the effort said. That component, which connects devices to cell towers, will gradually replace parts from supplier Qualcomm Inc. during a three-year rollout, Bloomberg reported earlier on Frid...