Any my.t customer (Fixed line, my.t home, my.t mobile) both in Mauritius and Rodrigues can use the app. All you need is a smartphone/tablet and any local SIM (my.t mobile or any other operator) registered under your name.
Note: You cannot manage a SIM registered in the name of a company/organization.
Yes, Wi-Fi or mobile data is required to use the app. telecom app is zero-rated i.e., my.t mobile customers will not pay data charges when using the app. However, data charges will apply when you go to other websites/external links from the app (e.g. Flight Info, FOREX, etc.).