If handsets can be delivered that cheaply, it could lead to another 100 million people a year getting their first phones, he said.
The thrifty price tag on the handsets is partly because of chip manufacturers' commitments to supply inexpensive silicon components, Brown said.
Speaking at the U.K.-based Institution of Engineering and Technology, Brown said that "it's beginning to look as if sub-$15 mobile devices might be achievable by around 2008."
Other projects aiming, but Brown pointed out a study by the London School of Economics that "found a 10 percent increase in mobile penetration creates a 0.6 percent increase in gross domestic product."
"In absolute terms that's a huge number. It's about a fifth of the average annual total global GDP growth," Brown said.
Brown said developing countries' governments now need to be persuaded not to tax mobile devices as luxury goods.
He said that in 14 out of the 50 developing countries the GSM Association surveyed, taxes represent more than 20 percent of the total cost of owning and using a mobile device.
"The association's economic experts believe that if ultra-low-cost mobile devices could be exempted from import duties and sales taxes," Brown said, "up to 930 million additional ultra-low-cost mobile devices could be connected in the 50 developing countries they studied between now and 2010."
"It's all too easy for those of us who live with seamless mobility every day to become blase about it," he added, "until we think about using seamless mobility to bridge the digital divide."
Gemma Simpson of Silicon.com reported from London.