The experiments have been done, in that there are offers like this overseas. Reportedly in some places it's a percentage discount if you bring your own phone, meaning it's a must-do if you by a big plan. In Asia, buying your own phone has become fairly common.

I think that they believe that the ability to offer customers free phones is a big win, and they could be right. They may well sell more plans with free phones and expensive plans than with expensive phones and cheaper plans. Once you offer free phones you have to subsidize the others as well, or so it would seem. The unsubsidized prices of many phones are quite scary to people, even though they will probably buy an $90 data+minutes plan with their $400 PDA phone, making the plan surpass the cost of the phone very quickly. Still, the customer may well like a $200 price on the phone more than a $400 price enough to eat that huge plan cost.