Africa showed the strongest gains over the past two years and more than two thirds of all mobile subscribers were from developing countries by the end of 2007, the ITU said.
This is "a positive trend that suggests that developing countries are catching up," the report said.
Mobile subscription growth stood at 39 per cent annually in Africa between 2005-2007, and 28 per cent in Asia over the same period.
India and China added 154 million and 143 million new subscribers respectively.
The global annual average growth rate stood at 22 per cent, the ITU said.
Mobile phones are eclipsing traditional fixed lines and in Africa they account for nearly 90 per cent of all telephone subscribers, the report said.
"The continued growth in the mobile sector is matched by no-growth in the fixed-line sector. Fixed telephone penetration has been stagnating at just under 20 per cent globally for the last years and growth has been below one per cent between 2005 and 2007," it said.
While developing countries have made great strides in mobile growth, a significant "digital divide" remains for internet use and particularly the availability of broadband connections, it noted.
High-income countries account for 66 per cent of all fixed broadband subscribers although they only represent 16 per cent of the world's population, while developing countries have just 1 per cent of fixed broadband users but 38 per cent of the global population.
"Low-income countries, where broadband access remains very low, risk falling behind in an area that is particularly important in delivering innovative applications and services," the ITU warned.
Some countries have made progress and the ITU highlighted Chile, Senegal and Turkey as states where almost all internet subscribers have now gone high speed.
"For more people to benefit from the potential of broadband and the applications that it can deliver, governments need to do their share to ensure that high-speed technologies become more accessible as well as more affordable," the ITU urged.