So anyway, I checked online and it said that I was eligible for an upgrade, so I did. With that is a 2 year service plan. Is that an extension on the existing plan?

Also, when you upgrade phones, does your number change if you're keeping the exact same plan, just changing the phone?

I have no idea. :\
Oh and do you keep your old SIM card or chip or whatever that thing is?
Or do they send you a new one with the phone?

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 =)