I currently have/use the T-Mobile G1 and was going to use the Curve as a backup but unfortunately my data plan doesnt work on it. It would be such a waste to use the Curve for simple phone use only and not even use it's messaging capabilities if you have the Blackberry plan.
One cool thing is if you are on the right plan you can use UMA and make calls over any Wi-Fi network. Very useful if you are running low on minutes or if you have terrible cell reception at home, etc.
Looking around $220 shipped obo

http://www.blackberry.com/select/blackb ... #start8320