Not surprisingly, Skype continues to erode the bottom line of mobile carriers as the popularity of it and other VoIP calling platforms continues to increase rapidly.

Research from analysis firm Telegeography confirms that though voice minutes saw a 5 percent increase in 2012 to 490 billion minutes, Skype alone saw its own usage grow 44 percent to a whopping 167 billion minutes. This increase of nearly 51 billion minutes is more than twice that achieved by all international carriers in the world, combined. As call volumes continue to grow, so do the challenges facing the international long-distance industry.

International migration, the rapid uptake of mobile phones in developing countries, and steady reductions in international call prices—especially in the form of flat-rate (and even free) calling plans—have contributed to traffic increases. Nevertheless, recent growth rates are well below the 13% average that carriers could count on to offset price declines over much of the past 20 years.

International voice traffic would have grown 13% in 2012 had it not been for the uptake of Skype according to the report, which shows that although international calls through the carriers have not declined, the number of callers choosing VoIP apps over carriers has risen.

The pressure on carriers is only going to increase as time goes on; VoIP apps will continue to grow in popularity and will reach a user base of at least one billion by 2017 according to an earlier report from Juniper Research.