Just took delivery of my dad's new Nokia 6800 from the UPS guy. =)
You can tell this is a "business" phone from the ground up. :D It's got a typical, no-frills design when you first look at it, and there's no camera built-in. In the short 15 minutes that I've played with it, here's what I think (compared to the 3650):
Display: although it has the same color depth as the 3650, it's not even close to being as bright, sharp and clear. But then again, since it's not a smartphone, you're not going to need an exceptional screen. I haven't tried looking at it in the sun, but it'll be nice if it has a reflective TFT like the 3650 so that you can see clearly without having to squint and turn the display at odd angles.
Construction: The 6800 "feels" a little more solid than the 3650. Now the 3650 is not at all fragile (as I mentioned earlier, I've dropped it too), but the 6800 just appears to be stronger, especially the back surface. It's smaller than the 3650 (duh!), but not as miniscule as some other phones out there.
Features: Comparing the 6800 to the 3650 in this aspect is just plain unfair. One is a smartphone, the other isn't. Enough said. The 6800 does have a stereo FM tuner though...something which the 3650 (and even the 7610) don't have, and it works really well. The sound through the speakers and the headset is very clear and sounds like any other stereo FM player. The fold-out QWERTY keypad is, without a doubt, much, much more convenient when typing out email/SMS messages than any other regular phone keypad (this was a key reason why my dad got this phone).
Connectivity: The 6800 is GPRS-enabled, includes a WAP (but not full-XHTML) browser, an email client, and SyncML to synchronize with a remote calendar/contacts server. It connects to a PC via either IR or a data-cable, but lacks Bluetooth.
RF: This should be one of the first things to look for in a phone, but I brought it up last since I obviously haven't had a chance to try that aspect of it within these first 15 mins. However, reviews claim that like almost every other Nokia phone, the RF and the voice quality of the 6800 is excellent.
Bottom-line: It's a nice phone. It has a modest, unassuming, professional look at first glance, and the fold-out keypad is a unique idea that keeps the size small, but packs in a huge convenience for text/email. The FM tuner makes it a cool toy too. :D