Just an update for anyone who is wondering. I decided to go ahead and try to upgrade my line, which is not the primary line on my family account, through Amazon, and then call and get them to price match.
The person on Amazon seemed a little reluctant at first, not because of any problem with my account, but because I apparently forgot to lead with the fact that I had already placed the order and was wanting that order price matched. They said, not realizing I had already ordered the phone, that I needed to wait for the phone to ship and see if they could price match it then, so she recommended I wait to order the phone. I then mentioned that I had already ordered the phone, and after a brief hold period, they came back and said I could get the discount.
I ordered the Gray one, but that's the one I was going for anyway, and they never asked about the color or anything, I just had to lead them to the correct page on Radio Shack. I did have to tell the rep to click on the Primary line for a Family account to get the correct price, but she never asked to verify the line I was upgrading was the primary line.
So, to make a long post even longer, I would go ahead and at least try to order the phone through Amazon, even if you aren't the primary line of a Family plan, and see if they will give you the price match. As I said above, they never asked about the color of the phone, didn't even mention it at all, so I would say you would probably safe with getting the white phone.
I guess I'm forfeiting my chance at the $50 gift card from Best Buy, but for $150 in savings over Best Buy's price, it's well worth it. Also, like others have mentioned when ordering from Amazon, they threw in a free car charger with my order. I love Amazon!