The top three operators -- Grameenphone, Banglalink and AKTEL -- have withdrawn their Tk 0.25 special tariff. The three operators control more than 90 percent of the market, or 40.14 million customers. The total market size is 45.21 million customers.The mobile operators had previously charged Tk 0.25. Now they are charging a minimum of Tk 0.40 to Tk 0.49 per minute. Grameenphone and Banglalink have recently increased their 'start-up' prices to Tk 900, which ranged from Tk 450 to Tk 500 a month ago. "Bangladesh has the lowest call rates in the world, which means that return on investment takes a very long time. This is why most mobile operators today are still not profitable," Ahmed Abou Doma, chief executive officer and managing director of Banglalink, said yesterday.