Email - Time Management

I remember taking a time management course many years ago.
I learned something about the phone.

Something like, everytime you stop working to answer a phone call, it
takes an average of 2 minutes to get back to the level of
concentration you had before the phone rang.

I was just wondering if there were any statistics about the effects
technology was having on productivity like email.  We must loose allot
of time due to people continually begin allerted of a new email.

Are there any statistics or websites that support this.

Thanks in advance
Just Me