The WSIS is the first summit to deal with the information society, including critical issues in the use and dissemination of information and communications technology in development programmes and policies.
The Summit will be held in two phases - first in Geneva starting December 10 and then in Tunis in November 2005.
"The existing digital divide threatens to exacerbate the gaps between rich and poor, within and among countries," Annan said and called on leaders from the developed and developing world, private sector and civil society to use the unique opportunity provided by the Summit to forge an action plan that will put technology at the service of human development."
Desai was the Secretary-General of the World Summit on Sustainable Development in Johannesburg last year.
"We are delighted Desai has agreed to assist us in the successful completion of WSIS," Yoshio Utsumi, Secretary General of the International Telecommunication Union, said.
The General Assembly has invited the ITU to take the lead responsibility in organising the WSIS, with full support from the UN family.
About 700 delegates are attending WSIS inter-sessional meeting being held in Paris this week in preparation for the Summit.