you cant swap numbers, trying to take one phone number from a line and move it to another line is a migration, you cannot do this. it is not the same as a port. They disallow this (although it can be done) to prevent what you are doing.....commonly referred to as phantom churn.
I can't speak to Sprint, but I know that with my own employer, a number and a contract are essentially one and the same. In most cases, canceling a contract is killing a number. Then reactivating a number is resurrecting the same contract. The two can't easily be divided.
Carriers long ago figured out the negative impact of allowing this kind of switcheroo, so they generally found ways to prevent it.
Exactly. I guess if someone could go for two to three months without service, they could get around some of this. Or if someone ported out to a prepay for three months, then ported back as a new line after the period in which the line would simply be reactivated, you could accomplish this. But then you'd end up having to buy a phone on prepay, which could cost you more anyway.
I run into people all the time who think a contract is merely something you assign to a number. Carriers nixed that a decade or more ago.
Imagine being able to defer your contract to another line on your account, effectively mortgaging your account. That would be a royal mess.