Earlier quoted context omitted.
At 160 bytes per text and 2T texts per year, there are 800 gigabytes of texts per day. Thus Carrier IQ is monitoring the equivalent of 1% of all texts across all phones. That is still quite significant.
The point isn't how many texts they're getting --- one would be too many. The point is "10 gigabytes per day of metrics" doesn't itself imply that they're getting message contents.
http://www.schneier.com/blog/archives/2009/11/leaked_911_tex...
Even so, I wouldn't put it past them to do keyword mining for mobile ads. That just seems like such an obvious potential use.