This mod allows you to know whether Gus will visiting Ginger Island that day by calling him on the phone. It relies on Content Patcher, so be sure to have it insalled before using this mod.
This mod consists of 2 parts: the folder without [CP] prefix provides a token for Content Patcher to identify whether Gus is on Ginger Island, and the other folder with that prefix changes Gus's dialogue on the phone.
How to use it: download the "Is-Gus-Visiting-Island" folder, copy and paste it into the Mods folder of Stardew Valley. For more information, check the official wiki page
It hasn't been tested roughly, and feel free to report any issues you encounter while using it.