Curve and 88xx are both great phones. The Curve of course has a camera on it and has more device memory. I happen to prefer the look and the keyboard of the 8830. Most people tend to have gripes with the keyboard though.
They are both great! Curve has a few more capabilities. I love my 8830 though! Either way, you won't regret the decision.
One more thing that I wanna add is that the 88xx will be more acceptable in a lot of buisness situations from what I've noticed. Lots of places don't want your phone to have a camera when you come in for a meeting and such.
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