"....One thing to be aware of - even though some phone plans give you "unlimited" data access on the phone, as soon as you start using it as a link for a computer, they want you to also have the normal data plan (some will hit you with major charges if they determine that you're doing this w/o having the plan)...."

This is a very good point. What Sprint likes to do is sell you one of the 'aircards' for 100 bucks then bean you for another 80 bucks a month.
The cool thing about the 6700 though is that it only has one NAI built into it so Sprint can't tell if you're teathering or not...hehehe. Haven't hacked...ummmm...looked into the 6800 yet to see if you can get away with it on that one or not. The PdaNet program that someone mentioned before does not use the wmodem program on the PDA, rather it uses the phones current, existing conection. Cool thing about that is 1) they're not gonna see that your are teathering, and 2) If you're connected to yer laptop via USB and not BlueTooth you can still be using it as a modem AND be using the ActiveSync program at the same time.
The other cool thing about these WM5 (and soon the WM6) phones is that if you know what you're doing, you can cook yer own ROM for the things. Right now my 6700, which is supposed to be a WM5 AKU2.2 device, has WM5 AKU3.5 and a whole bunch of the WM6 stuff squezzed in it. For more info you can eyeball http://www.ppcgeeks.com/viewforum.php?f=5&sid=59e5ad01e9fa7635af93e25c2d0c7fee