Barring calls from agents phones.

We are installing a new vicidial system at moment.
However it has occured to me tht the agents do not need to be able to dial out from their phones. Therefore it would be handy to be able to block their phones from making outbound calls, As the dialer passes them live calls and they dont have to use their phones to dial out.
Can anyone suggest a way to stop their phones from being able to access the outbound trunk whilst still allowing the dialer to work,.
Regards
However it has occured to me tht the agents do not need to be able to dial out from their phones. Therefore it would be handy to be able to block their phones from making outbound calls, As the dialer passes them live calls and they dont have to use their phones to dial out.
Can anyone suggest a way to stop their phones from being able to access the outbound trunk whilst still allowing the dialer to work,.
Regards