With call drops still remaining a problem, telecom operators like Bharti Airtel and Reliance Jio on Tuesday assured the government that they will invest a total of Rs 74,000 crore in the coming fiscal to upgrade and expand their infrastructure. Telecom secretary Aruna Sundararajan, who held a meeting with the CEOs of the telecom firms, said they presented their analysis of call drops which showed that it has stabilised but other problems like fading of voice calls have increased due to various issues, including some mobile phones not complying with required certification norms. She said that in Andhra Pradesh, Telangana, Chennai and Tamil Nadu circles, call drops are in the range of 30-33% but it is higher and \u201cvery bad\u201d in circles like Delhi, Mumbai, Uttar Pradesh and Bihar. \u201cTelecom operators raised the issue of non-availability of sites for installing mobile towers along with some other problems. Bharti Airtel said that they have invested Rs 16,000 crore on infrastructure and will be spending another Rs 24,000 crore in the coming fiscal. Reliance Jio has said that it will invest Rs 50,000 in installing 1 lakh towers in coming fiscal,\u201d Sundararajan said. Idea Cellular and Vodafone have also committed to increasing mobile towers in their network. \u201cTelecom operators said that call drop problem in mobile phones without Global Conformity Framework certificate is more compared to the certified devices. They raised the issue of illegal repeaters installed in networks (which) are creating interference and affecting call quality. We will look into enforcing rules more stringently,\u201d Sundararajan said. \u201cBesides, telecom operators said that there is new phenomenon they have found in India where around 400 callers use a mobile tower during the same time whereas in countries like China and others this average is in the range of 200-300. They are now discussing with equipment makers to handle this kind of issue,\u201d the secretary added. Telecom operators said data usage has grown six to seven times and continues to grow 20-25% every month but they were surprised to see a doubling of growth in voice traffic which has increase load on networks.