Some folks decided to study the calling habits of 5.3 million people over an 18-month period. 350 million phone calls later, they came to an almost obvious conclusion: Prepaid cellphone users make and return fewer calls than their postpaid counterparts.
You can click on the image to take a closer look at the graphs.
Initially the study done at the Aalto University School of Science and Technology, Finland, was intended to analyze reciprocity—the likelihood of an individual receiving as many calls in return as he or she makes. But during the course of the research, a clear difference was discovered in the calling habits of prepaid and postpaid users:
Postpaid users tend to be more prolific, having on average 5.41 people they call. Prepaid users, by contrast, have only 3.41 contacts on average (although the notion of "average" is a little strange here since there is a very long tail on these distributions).
Postpaid users also made about 10 times as many calls as prepaid users while 25 percent of prepaid users had odd relationships in which "one participant makes more than 80 percent of all calls."
Technology Review suggests that the differences in calling habits could be explained by the fact that prepaid users are more likely to be younger individuals, but I'd go as far as considering that the unlimited mobile-to-mobile or weekend benefits of postpaid plans may play a role as well. [Technology Review via NY Times Bits]