At the Des Moines corporate office, you have what is called a Direct Inward Dial (DID) number. This is just a fancy way of saying a phone number people outside of Seneca, can call you at. (Des Moines Waste Solutions does not adhere to this guide).
A lot of times people list it in their email signature as well.
Depending on your extension number, this will tell you what your DID number is:
Your DID is 264-(your 4 digit extension)
Your DID is 261-1(last 3 digits of the extension)
All other extensions
Your DID is 261-7(last 3 digits of the extension)
*With an exception, Darren Binning's DID doesn't adhere to this rule.