“Users with reading problems cannot use text menu based interfaces to store contact details, and as a result insert numbers directly to the phone. If a user needs to save a contact he will ask a literate colleague to assist with the procedure. So quite often users’ phonebooks contain a maximum of only 5-10 numbers. Research shows a direct relationship between the amount of contacts and the number of calls made. To increase the number of calls made, operators must ensure that it is easy and intuitive to use the contacts book.”

Quelle: http://www.receiver.vodafone.com/mobile-communication-in-the-developing-world