Forgive my ignorance, but you have to get an upgraded plan with the Blackberry, don't you? My wife and I have ATT, and Motorola v551 phones that we just use to make phone calls, take a pic or two, and play an occasional game of Jewelquest. I can access the net, but it costs extra. We pay about $70 per month. I wouldn't mind upgrading, but I don't want to pay any more than what we already are...
I think any carrier is going to charge an extra data plan for their smart phones.
I don't know about the others, but AT&T is $30 a month (for blackberries and iPhones).