International telephone call traffic is moving from traditional networks to IP telephony solutions. Data from the communications markets insight company shows that the annual growth of overseas calls has slowed to eight per cent over the last two years.

This is down from a yearly increase in international calls from telephones of 15 per cent over the 25 years before, TeleGeography has said.

Patrick Christian, senior analyst at TeleGeography, said that, while the recession had played a part in denting call volume, VoIP solutions are "a more permanent threat to international carriers".

Mr Christian explained that the VoIP carrier market is "siphoning away traffic" from the traditional telephone service sector.

He added that international call traffic to VoIP is rising and that the volume of overseas calls last year point to it playing an increasingly significant role in that market.

TeleGeography has predicted that the spread of alternatives to traditional telephone services will "present ever greater challenges to international carriers".

Returns from IP telephony solutions are continuing to rise and are expected to more than double over the next three years, market intelligence company In-Stat said recently.