Oliver welcome.
It seems to me that if indeed ou have this problem it is because can do it that they do.
In order to reduce it to a point where it does not matter, i'm not sure you will ever stop it completely, one can either become a cop or a coach.
Adopting the cop approach means that you need to install monitoring equipment and randomly monitor everyone. Those you catch, you initially have a quiet word with. If you catch them again it becomes a warning and if you catch them for a third time you let them go.
I guess what this amounts to is demonstrating very strongly what kind of behaviour is acceptable within your business. In my personal opinion, it is important however to let people make occasional calls as this demonstrates 'give and take' on your behalf.
Regarding the coach approach, what you do is monitor too. However, what you do is formally recognise and reward the additional work and results of those that do not make so many personal calls. This canbe by giving bonuses etc etc. I have to say though it is a strategy for a much longer time frame.
All in all, my advice would be start off by being a cop but then move swiftly over to coach. This way its a quick rap over the knuckles and then encouragement longer term.
Hope that has helped some
David |