The answer to this question varies by game engine and Vivox SDK version, as described below:
Vivox Unity 16.x
In Vivox Unity major version 16, iOS Simulator is supported starting with version 16.0.1, and the correct library for simulator use is loaded automatically when the Simulator platform target is selected.
Vivox Unity 15.x
In Vivox Unity major version 15, iOS Simulator is not supported and there are no plans to support it. We encourage testing on physical devices only when using this version.
Vivox Core
When using the Vivox Core SDK, the iOS Simulator is supported starting with version 5.22.0, and the correct library for simulator use is loaded automatically when the Simulator platform target is selected.
Vivox Unreal
When using the Vivox Unreal plugin, the iOS Simulator is supported starting with version 5.22.0.unr.0, but the correct library for Simulator use is not currently loaded automatically when the Simulator platform target is selected.
Developers can manually switch which Vivox IOS library is loaded by modifying the 'VivoxCoreLibrary.Build.cs' file to load the included simulator library libvivoxsdk-simulator.a instead of the usual libvivoxsdk.a typically loaded for the IOS platform target.