I am a call center manager at a telecommunications provider, and I would like to know if it is possible to calculate...
or forecast call volume/customer contact volume rate?
Without knowing specific information about your call center, I will assume that the types of contacts you are referring to are customer service in nature and not inbound sales calls. You'd want to forecast each of those types in a slightly different manner.
Customer service call volumes are usually forecasted as a ratio of calls to the customer base. For example: If you have 100 customers and 20 of them call you each month, you would have a call ratio of .20. If you were to increase you customer base to 150, and made no other operational changes, you might expect to receive 30 calls (150 x .20 = 30).
By calculating your current ratio and trending any historical information available, you will be able to determine the correct ratio to project future call volume. Be aware that you must take into account any irregularities such as extraordinarily high or low contact volume days, when calculating your ratio.