Did you ask the question because you are you interested in getting a new phone? If so, you'd be interested to know that you definitely don't need to pay off your entire Tab to qualify for a new one on the new Tab Small or Medium :)
Only way to get billed for the tab is cancel. If you wish to upgrade you can use the same moneys towards your phone instead of paying off your tab. It would work out to the same thing regardless of what phone you get.