purchasing a blackberry curve 8330 off ebay

I am not due for an upgrade until december of 2011, and my current phone is starting to not work properly. I found a few Blackberry Curves 8330 on ebay for a decent price and I was contemplating getting one. I am aware i will have to upgrade my data plan to an unlimited one, but i was curious if i would be able to activate that blackberry or if it was too old of a version to work correctly.

Another option was going off of my parents plan and going onto my own, if i did that would i still have to wait until December for my upgrade?

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