If using more bandwidth costs the cell carriers more money, perhaps they should charge people for using more bandwidth. This is the only industry I've ever heard of where when demand exceeds supply, they simply refuse to increase capacity.
I suspect the hesitance to have prices mimic costs is that fact that the [oligopolistic] carriers don't want to lose money from one of their highest revenue users who incidentally use very little bandwidth -- corporate blackberries. In fact they are designed to be use data minimally for most users, e.g. only text parts of emails are downloaded at first, email is push rather than pull. If the carriers actually had a system which tracked costs, the $5 verizon "feature phone" plan would cost $50 and the $50 BES blackberry account would cost $5 and accordingly substantially screw with their highly precise and profitable price discrimination. Granted, they could have a segmented system where blackberries existed outside of it, but why rock the boat when they're making tons of money and only stand to lose it in this situation.
Keep in mind, all of this price discrimination is made possible by the carriers being able to identify the phone you are using and how you are using it since they only allow their phones on the network generally. GSM has some minimal exceptions to this, but even if you bring your own equipment, they might have a database of its IMEI and charge by that and/or identify that you're accessing an exchange server/skype... Don't get me started on MEID/ESN databases for CDMA, it's even more despotic
Also, more specifically in this context re: 3G on skype, consider that's it's not a data issue per se, but more a money issue for minutes, after all, look into how verizon blackberries handle skype traffic and minutes in the context of high value plans...
My two cents
I can't use my Encyclopædia Britannica DVD from a few years ago, because it's incompatible with modern operating systems..
You could use a VM, if you really wanted to
He has not acquired a fortune; the fortune has acquired him. -- Bion