According to the reports from 9to5mac, iOS 12 beta 5 further hints that the new upcoming iPhone’s model to come with dual-SIM support.
A component of the system responsible for the generation of diagnostic reports includes new references to “second SIM status” and a “second SIM tray status”. Another component references a “dual sim device”. Those references are clearly an indication that iOS is being updated to run in a future device with support for two SIM cards, as seen in the screenshot below. The mention of a “second sim tray” indicates it would, in fact, have two physical SIM cards instead of a regular one and an e-SIM as the second.
This is the very good news and a major update for Apple launching the iPhone with dual SIM functionality. This feature would allow users to switch two different carriers SIM cards in one device and no need to carry other extra phones to have a different SIM.