iPhone 5s

If you are buying it outright, and if it's about the same price, you may want to buy it from the Apple store if Apple is selling them unlocked (as they have been doing with the previous iPhone models). Just a thought ... If Koodo sells it for $50 less then you can always use the saved money later to unlock the phone. If you want to use whatever is left available on your tab you can put that towards a 5S from Koodo when they come out (as Paul mentioned). You would get 15% off so that's something depending how much room you have on your tab.

If you know why did you ask man? Lol

Yes your tab owing is tied to your account not the phone. You can buy it outright or even use remaining tab amount you have that will bring you to the maximum of whatever tab you choose.