When this is a policy decision, we must be very strict about it. In my organization, people were initially allowed to take cell phones inside the plant, and suddenly a decision was made to ban it. In such cases, those who have been used to it would either protest (through Unions or individually) or would conceal phones in various ways. Talk to the Unions first on this and seek their cooperation, which we also did. The signboards will also be necessary all over the plants.
The security checks should be vigorous, and staff/supervisors at all shop floors should be entrusted with the responsibility to watch and inform the offenders. This is what we do—after a few warnings, we now impound cell phones. You know what they are doing now; once they take the cell phones inside, they keep them in their pigeonholes. They take the SIM card alone inside and use it! We have then ordered the security to conduct surprise checks in their pigeonholes.
Initially, it will be difficult, but once they realize, the cooperation of the workers will be there.
All the best.
Regards,
Ganesh