Where to buy new phone

Hello all...I am currently an AT&T wireless customer. I am eligible for an upgrade in October. I was going through AT&T's website and am pretty sure I'm gonna upgrade to the BB Bold. Now it looks like if I upgrade though AT&T directly, I will be paying $400 out of pocket with a $100 rebate with a 2 year extension. I was looking at places like newegg that offer AT&T service and their price for the Bold is $100 out of pocket with a 2 year extension. My question is...is there any advantage or disadvantage in upgrading and extending my contract directly though AT&T as opposed to a place such as Newegg?? If I go through Newegg, will I still recieve the same service options such as data plans, insurance, etc?? Or am I just looking at the pricing information completely wrong?? Sorry for the naive questions, but thanks in advance.