Open Beta 7, the latest in a series of in-testing stock ROMs available to owners of the OnePlus 6 to test out, contains an interesting new feature. It is OnePlus Roaming, a SIM-independent form of access to the internet that can be purchased directly on the 6 - and only the 6 for now.
https://www.notebookcheck.net/Latest-Open-Beta-for-OnePlus-6-introduces-new-service-OnePlus-Roaming.366071.0.html