In the eight circles where MTS is operational, this will be optional, while in the remaining circles, it will be mandatory or the user will lose his or her number when the CDMA service is shut down to make way for 4G. Read more at http://rtn.asia/t-t/19146/reliance-cdma-switch-gsm-plans-4g-upgrade-jio#jJ6jD6vOPlHmbDka.99