You will most likely be answered to by a member of your representative's staff. She/he is probably an intern, or recent college graduate. Her/his job is to tally up all the calls per day and deliver a report to the senator the next day.
Clearly state the issue you are calling about (for example: "Hello. I am calling about to express my concern about X.").
It is also helps to give your name and your address, as proof of the fact that you are a constituent of North Dakota, whose concerns have priority over those of non-consituents).