determining statistical significance

Yep, you can do anywhere between a p of 0.10 and 0.01 if you choose to change your condfidence interval.

Edit: Are you also after things like...the average call time is 3 minutes with a standard deviation of 30 seconds. Meaning 99% of the time, calls fall between a duration of 1min30secs and 4mins30sec?

Just remember that 99.7% of data fall within 3 standard deviations of the mean.