Dear Atul Nipankar,
To prohibit the use of mobile phones in the workplace, I found other BPOs providing the lockers to their employees. Employees are required to keep the phone in safe custody and after completion of their duty, they can take out the phone and carry it with them.
The second provision I found was to block the camera with the security tape of the company. They can use the smartphone but without a camera.
Notwithstanding the above suggestions, if you have a fear of employees taking photos of the screen and thereby gaining access to the information unauthorisedly then how far these suggestions will work remains to be seen. This is because nowadays the spy cameras are available for the price as low as Rs 1,500/- There are spy pens, spy watches, spy lockets and so on. While you may impose the ban on the use of the camera-phone, how can you ban carrying spy-pen or spy-watch? Those who want to gain access to the information and further leak it, they will do it anyway.
Thanks,
Dinesh Divekar