Hi Prakash,
I think TSP API can achieve your task.
An API that allows Teleconferencing Service Providers to integrate their audio conferencing service with WebEx. WebEx TSP Partners can offer WebEx to their customer base while retaining the audio conferencing business and the customer relationship. TSP API enables tight integration with WebEx, including active talker, mute/unmute, call in, callback, on-net callback, video switching, sub conferencing, invite by phone, etc.
Please check the section Site Level Configuration were the WebEx Meetings Account Manager provisions your site with the Telephony configuration options like Maximum Number of all Callers and Major Country/Region
Thanks and Regards,
Geevarghese