I'm planning to preorder an iPhone XR but am unsure which carrier model to get. I currently am using tmobile but may switch to another carrier soon as my data connection has not been that great. Not 100% sure which carrier I'll switch to and wanted to get a model that's compatible with any carrier. Anyone know which models for the XR are compatible with all the carriers in the US? Asking because I don't see an unlocked version as an option currently in the Apple Store App.