your number stays the same. and the 2 year plan just starts over. it doesn't add on. so starting today (or whenever you upgraded). the next 2 years is when your contract is over. but i realized that you don't have to wait until your contract is over to upgrade. you can be upgrade eligible after a year or even less into your contract as long as you hold a good record on paying your bills on time or whatever. but when you do upgrade, you do get to buy another phone for cheap or even for free, but you have to start the 2 year plan over again. not sure if you already knew that but just in case =)