Md. Touhidul Islam, and Md. Asfaqur Rahman. “Effectiveness of Push (SMS) Service: A Study on Grameenphone and Airtel Subscribers of Bangladesh”. Global Journal of Management and Business Research, vol. 15, no. E7, May 2015, pp. 17-43, https://journalofbusiness.org/index.php/GJMBR/article/view/1785.