Well, if u ask me. i would say you have to see how big/small ur business is? go according to that!
if lets say your business is a big one then u can go for business plans in telco but if ur business is kinda newbie or small i think the best is you provide the limitation, for example you limit each person to rm100/ month. Guess that is fair enough! and people i would suggest everyone to use the technology provided to us. Nowadays, people are looking forward to deal in whatsapp, telegram n viber. we even have calls in that! free of charge!
Hope it helps! Good day peeps :)