https://techcrunch.com/2018/08/01/ios-beta-hints-at-dual-sim-iphone/

Apple released the fifth beta of iOS 12 a few days ago. 9to5mac discovered strings in configuration files that reference dual SIM devices. You should expect at least one new iPhone model with two SIM trays.

Apple is said to unveil three new iPhone models in September. In addition to an updated iPhone X, the company should announce a bigger second generation “iPhone X Plus”.