This is according to the International Telecommunication Union (ITU), which said that better and more extensive fibre optic cables were required if "chronic problems of network unavailability" were not to become worse.
It is expected that the number of smartphones in use worldwide is expected to quadruple by 2015, from 500 million to two billion.
Dr Hamadoun Toure, the secretary-general of the ITU, said: "Mobile operators have been investing billions to upgrade and improve the capacity and performance of their networks, but in some high-usage cities, such as San Francisco, New York and London, we are still seeing users frustrated by chronic problems of network unavailability.
"Robust National Broadband Plans that promote extra spectrum and the faster roll-out of the fibre networks which are essential to mobile backhaul are vital to support the growing number of data-intensive applications."
