D. Carboni, S. Sanna, and P. Zanarini. MobileHCI '06: Proceedings of the 8th conference on Human-computer interaction with mobile devices and services, page 169--172. New York, NY, USA, ACM, (2006)
S. Gaonkar, J. Li, R. Choudhury, L. Cox, and A. Schmidt. MobiSys '08: Proceeding of the 6th international conference on Mobile systems, applications, and services, page 174--186. New York, NY, USA, ACM, (2008)