How much time does the average person talk on the telephone?

Its difficult to know for sure as the studies I've found cover either the workplace or private usage but, not, apparently both. Ofcom Uk reports 28 minutes (implied) private. 15 on Landlines and 13 on cellular.

Jenni Morgan at Mars reported 41 calls per office worker per day at just over 2 mins per call. Creative workers are closer to 48 calls each of which are longer