I've heard it before from some staffers' own mouths - E-MAIL is the LOWEST on the "pay attention" scale for these people for communication from outside the office. Hard copy (i.e. letters and faxes) AND phone calls get heeded. E-mail, especially from non-constituents either gets ignored or gets deleted straight into the "trash" box.
Bump for emphasis.
Dealing with phone calls requires time and effort and involves personal interaction. Definitely the way to go...