What is the average time duration in your opinion to finish a routine customer call?

This is a very industry specific question , for example1.
In an organization where the business is generated by cold calling a successful closure of sales call varies from30 seconds to30 minutes.2.
I an organization's customer service department time duration is about2to3 minutes.
So best way to know the average duration of a routine call in any business is to compile data of the calls for at least previous couple of months and draw a conclusion depending on the results availble.