Mobile network traffic growth

It's interesting to look back on the growth of mobile networks so far.  Here are some numbers on cell sites, subscribers and voice minutes of use, extracted from CTIA data by Andrew Odlyzko.

      1991              2006

Subscribers            6.38 M          219.7 M

Cell sites                6,685           197,576

MOUs                    5.2 B           858 B

 Over 15 years, voice traffic grew 165x which is 41% CAGR. 

As an aside, it's interesting is to separate the growth in capacity due to more cell sites from the growth due to better wireless technology.  Over the 15 year period 1991-2006, we got a 30x growth in the number of cell sites, or 25% CAGR.  That suggests improvements in wireless technology (the transition from 1G AMPS to 2G and 3G systems) provided for only 5.58x of the increased traffic, or 12% CAGR.  This surprised me.  It can't be due to uncounted data traffic as data traffic was a small percentage of the mix in 2006. If true, it's rather embarrassing for the 2G and 3G equipment providers.  Any suggestions?

There's a different view in this study of available mobile data download speeds done by Novarum Inc.

This shows available download data rates doubling in a little less than 24 months, or ~45% CAGR. However, this is measuring available bandwidth, not actual traffic.  None-the-less, it's suggestive of capacity as these measurements were made on live networks during business hours.