I went to Cingular's site (partly because I'm already a Cingular subscriber.) And I didn't need a calculator to do the math:

crackberry = ($300 Crackberry with 2 yr contract) + ($200 4GB iPod nano) = $500
treo = ($400 Treo 750 with 2 yr contract) + ($200 4GB iPod nano) = $600
cing = ($400 Cingular 8525 with 2 yr contract) + ($200 4GB iPod nano) = $600
iphone1 = (4GB iPhone with 2 yr contract) = $500
iphone2 = (8GB iPhone with 2 yr contract) = $600

therefore:
crackberry = iphone1
crackberry [lessthan] iphone2
treo > iphone1
treo = iphone2
cing > iphone1
cing = iphone2

Then comes accessories like car chargers and USB cables -- which most people already have for their iPods -- that will increase the overall total cost of the other "smart" phones. Oh, and the iphone2 configuration, since it's 8GB in capacity, while equal in price to the Cingular and Treo smartphones, is actually the better deal.

Personally, I'm interested in getting an iPhone, but I have an issue with being too tied to my phone, which I currently use only minimally anyway. (less than 30 minutes per month.) I have about 6 people in my phone's memory, use my 60GB iPod photo for appointment reminders and contact lookup, and my Newton MessagePad 2100 for note taking. (In addition, I have plenty of extra space on the iPod that I frequently use it to shuttle & backup files from Point A to Point B.) For me, it works fine, so no need to upgrade. My wife, on the other hand, will probably be getting one.