I think that part of the reason for capping the data plans is that many smart phones, like the droid, have Skype or other VOIP applications built in. Using Skype, why does someone need to pay for a voice plan?
Since we have made it impossible for ISPs to charge for the type of packets, that is, they cannot charge more for VOIP packets than streaming media, they will lose money on voice plan minutes if customers start using Skype or other VOIP service on their smart phones.
However, getting rid of unlimited data plans hurts thoses who decide not to use VOIP services and pay for unlimited minutes.
Companies like AT&T and possibly Verizon and others should offer a pricing structure that would allow unlimited data with unlimited minutes. So a customer can max out with unlimited voice, text and data for bundle price of $119.98 ($89.99 + $29.99). If you have a plan with less minutes, less text, the unlimited data would cost more. For a 450 minute plan without text (currently $39.99) an unlimited data plan might have a price tag of $69.99 for a total price of $109.98.
This would allow unlimited data plans to stay available and allow the phone companies to not lose money if everyone starts dropping minutes by using VOIP services.