i'm confused. are you talking about the data that some isps use now?
phone data are just sold by megabytes, because speed is irrelevant. your speed is 3/4g.
ALLLLLL isps sell internet by megabit. because your data is (normally) infinite, and you are buying speed, not amounts of data.
if your home has a 3 megabit package, you are getting a max 375killabytes of speed per second.