you best bet is to probably buy it outright. Becuase i know on some carriers if you cancel they wont give you service again for so many months.
And etf 175 cost of new inc 200 + new act maybe 36.
new inc no contract 529
I do believe you can cancel one line and just make another the primary but like i said not sure if they will let you open another line.
Blackjack1 => blackjack2 => Blackberry Curve => Iphone 3g => Droid =>Incredible.