What you get in the box:
Phone, battery, belt case with magnetic closure (not bad I might add for an included case), wall charger, MiniUSB sync cable, stereo headset, CD with Outlook 2002 & manual I assume (haven't broken the seal).
*NOTE: No miniSD card is included as appears to come with the other re-branded versions.
Phyisical quality of phone is very nice. It's solid in your hands. It's small. The keys have a good response to them, if a little bit small. I do find myself hitting the "home" key on accident instead of the "select" soft-key on ocassion, but this will be gotten used to, no big deal in my opinion.
Screen is very good. Perhaps not quite as nice as the MPx200 (at least as I remember it, it's been 6 months since I had it) and not quite as nice in some regards to my current V600 screen, but it's still VERY nice. It's clear to me that the screen has been tuned "down" for the sake of battery life. Screen is also actually readable outside, even in the sun! However, if you have polarized sunglasses like I do, it's hard to read the screen with them, but that is the case with many LCD's, I don't think that's an issue with the screen on this phone.
Call quality is excellent. I give it a 10 out of 10 so far as compared to all the cell phones I have had before. Each generation seems to get better, and this is no exception. Callers hear me loud and clear (one caller told me, and I quote "as good as it gets" about the clarity of the call). Ring tones are nice and loud, even at 4, so I know it goes higher. The vibrate on this phone is very good, it will rattle on your table.
RF seems to be strong as based upon 2 things:
a) bars (I know, not an absolute measure by any means) are often full in places where my MPx200 got 2 or 3, and it appears to get full bars when my v600 does not. As with any GSM phone, the bars are not a perfect measure of RF, but I did notice this. I think it has a better antenna.
b) calls held nice and strong today in my car in place I would expect minor breakup (downtown Seattle to be specific). AT&T has vastly improved coverage in between buildings in Seattle in the past year, but I did have a nice good quality call today in areas that have formerly given me trouble.
The true test will be over a few days and weeks. But out of the box, this beats the MPx200, no question as far as RF & Call quality go.
Speed It's fast. Much faster than the MPx200. I notice it's faster. A few lags here and there, but I don't notice the lags as much, and they are where you expect them: after waking up from sleep mode, or turning on Bluetooth, things like that. The lag is not all gone, but it's much improved so far.
mMode is FANTASTIC on this device. The new mMode stack was one of those things everyone complained about with the MPx200 (if you were an AT&T customer) and I must say it looks FABULOUS on this phone, especially the sites through mMode such as CNN etc that are specifically formatted for mMode. I think I will bump up to the unlimited mMode plan, I might actually use it! And it actually seems faster than my v600 on mMode, and faster certainly than the MPx200. It's not snappy on regular web pages as you would expect with GPRS, but not bad on pocket pages.
Tethering. I tethered this with my iPaq hx4700 with no problems. Once I got the correct dialing string for the phone it connects fast and I had no trouble connecting and checking email. The connection string to use is *99#
Camera: Well...it aint grand. But whad did you expect?

I will say this, I haven't really taken any outdoors yet in good light, so it's probably going to be better in those conditions than in my office at night, but here are some shots from the camera:

A little blurry...gotta work at holding my hand really still!

Still a little blurry..keep it steady...

Ok, that's a little better. Maybe with practice it's high quality?
And for comparison, here is a shot from my V600 VGA camera of the Smartphone Thoughts website seen in picture #1 above:

The v600 doesn't have a great camera, but this shows you that the SMT5600 is a tad bit worse if you compare them to each other.
Video: Fun. No idea how to convert it to use on my computer, but it will be fun for video MMS's friends who have phones that are compatible. It's actually really fun to use as a way to distract your 3 1/2 year old...
Gripes? Minor at this point. You still can't seem to configure your POP3 email through the phone unless you use AT&T's online configurator (http://www.attwireless.com/smartphone) and even that doesn't have the SMT5600 as an option yet, but the MPx200 option works fine of course for the Audiovox. Also, I can't figure out yet how to make a speed dial for just Bluetooth. I can do it for "settings" and then 2 more key presses to BT, but so far no direct BT "on and off toggle" which is what I would like. Perhaps it's there and I haven't found it yet. Also, I seem to remember a key lock (hold and press the # key?) on the MPx200 to activate key lock. Of course on a flip phone it's not a big deal, but the only way to do it now is to go through the "Quick List" menu. No big deal, but again, a few extra keystrokes.
At this point that is all I have to say. So far, so good. Looking forward to putting this to the test, but I like what I see!
Feel free to ask me questions, I will do my best to answer what I can!
EDIT: I just had to add this...I just downloaded & installed betaplayer for Smartphone:
http://betaplayer.corecodec.org
and then installed the 160x216 24fps 192Kbit/s B-Frame 2-pass XviD of the Matrix preview...all I can say is: where do I get a 1 gb miniSD! HAH, it's really great quality. Sound is very nice through the speakers. I am very impressed with that.