Most of Apple’s key executives and engineers are anonymous, never appearing on stage or in news stories, but Rubén Caballero is an exception — a long-term wireless engineering VP who helped develop multiple iPhones dating back to the original model, and reportedly red-flagged the iPhone 4’s antenna design internally before it became infamous. Now Caballero has joined Microsoft, his LinkedIn page confirms (via Bloomberg), and his new role could be significant: He left Apple during its 5G modem development drama, and is likely to bring significant cellular and related wireless expertise to his new employer.

Caballero’s new position includes hardware design and technology engineering for Microsoft’s mixed reality and AI division, which he notes will include “HoloLens, Special Projects and more to come” — the sort of open-ended purview that suggests eventual involvement with many Microsoft-branded devices. During his 14 years at Apple, Caballero was significantly involved in the wireless chip and antenna components for not only iPhones but also iPads, Macs, recent Apple TVs, and the final AirPort wireless routers, which is to say that his work for Microsoft may eventually include improving the cellular or wireless performance of Surface computers and AI-fueled “smart devices,” in addition to mixed reality hardware.

Today, HoloLens is one of the key Microsoft products that could benefit from his cellular engineering expertise. The current-generation headset uses Wi-Fi and Bluetooth for communications, but it doesn’t have integrated cellular capabilities — something that the last two all-in-one HoloLens designs might struggle to deliver given their placement of all hardware on the user’s head. While cellular phones are widely considered safe for brief periods of direct head exposure, radio emission guidelines typically recommend limiting up-close ear use to short periods of time, with headphones or speakerphone modes as options.

Leading AR headset makers are all working towards lighter, more comfortable wearables with integrated high-speed wireless connectivity, though companies may vary in choosing Wi-Fi (such as Wi-Fi 6E), one of several 5G cellular frequency bands, or a future Bluetooth standard. In any case, familiarity with cutting-edge antenna and chip designs will be critical for engineering next-generation devices with smaller sizes and less power consumption.

Immediately prior to leaving Apple last year, Caballero was reportedly sidelined in efforts to internally develop the company’s 5G modem, as the company opted instead to purchase Intel’s 5G smartphone modem business for senior engineering VP Johny Srouji to lead. He subsequently became an adviser or strategist for four different companies, including at least two staffed with former key Apple employees — wireless venture Keyssa, backed by iPod and Nest pioneer Tony Fadell, and secretive startup Humane, run by iPad UX leads Bethany Bongiorno and Imran Chaudhri. It remains to be seen whether Caballero will continue to participate in those ventures during his tenure at Microsoft, but they’re currently listed as present rather than past tense on his profile.