Inserting Blank Line into File (sed/awk/?)

[Tim Evans]

I would like to be able to insert blank lines at regular intervals
in a structured file.  Specifically, I want to place a blank line after
every third line in my input file.  Every third line in the input file
begins with a specific character string.

Here is an example input file:

Name: data ...
Addr: data ...
Phone: data ...
Name: data ...
Addr: data ...
Phone: data ...

What I want as output is:

Name: data ...
Addr: data ...
Phone: data ...

Name: data ...
Addr: data ...
Phone: data ...

If you reply via E-Mail, please use the address *BELOW*.

Thanks.
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