On modern phones you don't even have to switch carriers. You can have multiple lines on a single phone and use them at the same time. Ie I can use one phone to text from my work number and my personal number at the same time. Or if you live/work near a country border you can text/call/data from either line at the same time.
No Google fit connects into this. It allows apps like Fitbit, Samsung health and Google fit to all have the same data.
So I don't have to tell my watch how much I weigh, my Fitbit scale tells the Fitbit app and that syncs with google connect so that Samsung health can then pass that to galaxy 5 watch.
In english a double negative is a positive, and is syntactically incorrect.