Report Suggestions?

I am in the IT department of a call center. We can import the workers phone records into Excel from the VoIP manager. What we want to find are gaps between calls and I was wondering if someone could point me in the right direction.

the data is:

Time, phone number, call duration

each call is a separate row.

So I'd like to be able to use some way to go down the calls and find a gap. Let's say:

3:00, 555-1212,3:47
3:25, 555-2345, 2:45
3:55, 555-4567,1:03

then we have an employee with long gaps between calls. With all the noise in a large call center someone goofing off can remain under the radar if they look like they are doing something.

So can it be done in Excel or a 3rd party reporting tool?

Something like this?