Apparently, this is not an aberration. According to a recent research report from Juniper, such high levels of growth are expected to continue on the mobile VoIP front.
According to the latest report, here are some numbers
Average estimated annual growth rate in mobile minutes : 100%
Global Mobile VoIP minutes expected in 2010 : 15 billion
Global Mobile VoIP minutes expected in 2015 : 470.6 billion
US Mobile VoIP minutes expected in 2015 : 135 billion
Expected cost of mobile VoIP over Wi-Fi to operators : $5 billion
A growth from 15 billion minutes to 470 billion minutes over a 5 year term is huge. This could definitely mean that services like Skype and Nimbuzz are the ones to bet your money on in the next five years.