Nokia 6682. It's not available from all/many Cingular stores as of last week, but they claim to be getting more in soon (apparently there was a firmware problem with some people's SIM cards).This phone has regularly been reviewed as one of the "best of breed" for smartphones that aren't hardcore PIMs (a la Treo, Blackberry). It's a phone first and foremost, but has Symbian OS, and there are a ton of apps you can add to it. Plus, great bluetooth compatibility and a reasonable size (not quite as small as the V551 you have, but much nicer screen IMO... and a better camera.)Probably the best phone (PHONE!) Cingular has at the moment. If you can't find one at the Cingular store, you can order it from Nokia's site directly and apparently, keep your existing plan (I think... there's a phone number to validate that as you get through the checkout process.) Or just buy one anywhere, as long as it's unlocked, your Cingular SIM will work as long as it's not one of the "3G" cards.
www.nokiausa.com