http://www.ourwebhome.com/TENP/Recommended.html

Site of recommended prefix names, and both DUdley and DUpont are acceptable. (You wouldn't want a phone prefix named GLockenspiel - too hard to say - or SChmidt - people would think to dial SH instead.)

Think I may have uncovered something here:

https://groups.google.com/forum/#!topic/comp.dcom.telecom/0wUIrjDQbVg

If North Las Vegas/Nellis AFB was served by a different phone company than the rest of Las Vegas, they would have had their own switchboard (exchange). It might have been Continental Telephone which at one time served smaller cities or carved up territories out of large cities. Perhaps to keep things simple (in their thinking), they went with DUpont. I know for sure that Los Angeles once had Pacific Bell Telephone (PT&T) and General (GT&E) which held monopolies in their own sections of the city, and woe unto anyone who lived in one area and wanted to call someone in the other - it would be charged as a toll call, even if it were to your cousin Manny across the dividing-line street! So if you called from a DUdley number into the DUpont area, it would cost an extra nickel or something.