1. Business case studies: using technology to improve economies (2015). http://businesscasestudies.co.uk/vodafone/using-technology-to-improve-economies/
2. Kochi, E.: How the future of mobile lies in the developing world (2012). http://techcrunch.com/2012/05/27/mobile-developing-world/
3. The Economist: Airtime is money (2015). http://www.economist.com/news/finance-and-economics/21569744-use-pre-paid-mobile-phone-minutes-currency-airtime-money
4. Safaricom: M-PESA (2015). http://www.safaricom.co.ke/personal/m-pesa
5. Cimato, S., Yang, C.-N.: Visual Cryptography and Secret Image Sharing. CRC Press Inc., Boca Raton (2011)