It was not unusual to have that happen at NW, at least on the normal line. However, the problem I have had with DL is their agents hanging up on me during the call. It has only happened with DL. Not on any other airline or even with any other call center of any sort. It has happened several times, most recently as a DM-to-be in February. A ticketing snafu was preventing OLCI and the delta.com support agent just hung up on me when I said I didn't have an internet connection available when I called.