I think there is no unique solution to Ogie’s question. Certainly, at one critical end, the no. of simultaneous calls can just be the no. of calls if all the calls are made at the same time. At the other end, these calls may spread evenly among the day. In other words, you can only get the upper and lower bounds to the answer:
upper = no. of calls during the day
lower = no. of calls during the day * average ACD (say in sec)/24*60*60 sec
Please correct me if I’m not right.