Doesn't work out well in practice...
Here's the problem...
Phone and data pricing isn't a simple problem to solve.
First, you have to remember that the phone company is a *for* *profit* organization, so they want to make money.
Second, they are spending billions to upgrade their network to handle 3G+ traffic. All of this to get consumers to use their networks.
And consumers like having a set monthly price, even if it means that they may be paying more in the long run. (I know I have a cow when my phone bill doubled one month because my wife who never used to text started texting and well exceeded her plan's amount.)
So the phone company does some voodoo calculations and determines that $50.00 a month for an 'all you can eat' package is profitable because the majority of the users don't send that many texts or use internet features. At the same time, the networks can handle the traffic loads and still have room for xx% growth based on the estimated usage by their customers....
But these are only estimates... you set a price too high, and customers flock to your competitors. You set it too low, you go broke and you can only change your rates on new contracts so you're stuck.
Add to this... people who want to download and play movies on their phones. (Ebooks too but they're not as big.) All of this data usage by a larger segment of the population means that the initial estimates are way out of whack.
The simplest solution is to throttle. Many people won't notice being throttled. Those that do will change their usage habits. (Don't use 3G to download the movie, do it via wi-fi at home instead.)
Trying to do a 'base + ' package doesn't work well. How would you feel when you get your phone bill and its 3x your normal bill because little Billy was playing online games with his friends and also downloaded 4 full length cartoons a day?
I know throttling sucks, but its a no brainer for the telcos to implement.