1. Marczewski, A.: Gamification: A Simple Introduction & A Bit More. Amazon Digital Services, Seattle (2012)
2. Clark, J.: History of Mobile Applications, MAS 490: Theory Practice of Mobile Applications. University of Kentucky, Lexington (2012)
3. Treo and Centro: Treo and Centro Software titles.
http://blog.treonauts.com/2008/01/treo-and-cent-1.html
(2006). Accessed 15 Sept 2016
4. Litchfield, S.: Symbian Market share analysis from ABI. All About Symbian.
www.allaboutsymbian.com/news/item/5059_Symbian_market_share_analysis_.php
(2007). Accessed 15 Sept 2016
5. Mogg, T.: SFO trials beacon-based navigation system to help blind visitors explore terminal. Digital Trends, 4 Aug 2014.
www.digitaltrends.com/mobile/sfo-trials-beacon-based-navigation-system
. Accessed 15 Sept 2016