T-Mobile did not invent month to month
T-Mobile did not invent month to month, they were just the first big carrier to realize the old business model was going to eat their lunch as people were getting fed up with contract and hardware lock-in as well as the companies not honoring rates, overages and contract plans and even the end of contract and still trying to extort cancellation fees (see previous stories about cable companies doing same as well)
T-Mobile also had a program that a lot of other mobile carriers had: pre-paid. I used that for years until my pre-paid reached the first tier contract price that offered more. At that time I switched to contract.
Since then I haven't had a mobile contract in 3 years and never will again. I'm finding each carrier eventually tries to screw you and that's when it's time to move on.
Biting the hand that feeds IT
