At the time this article appeared, only men had the right to vote throughout most of the United States, and most calls were connected by female operators working at centrally located manual switchboards.
Telephony, June, 1908, pages 373-374:

IOWA politicians recently found the telephone a most useful and effective means to induce voters to go to the polls on election day. At Des Moines arrangements were made with the telephone companies and the morning of the fateful day the operators at the exchanges called up all the voters who have telephones and courteously reminded them not to forget their duty as citizens. Candidates on both tickets agreed to the plan whereby the operators called up every subscriber. If the telephone was answered by a man he was greeted with a polite "Don't forget to vote to-day." If the lady of the house answered the bell she was told to "Remind Mr. Blank to be sure and vote to-day."
    The result was that a much larger vote was polled than was anticipated. The telephone call proved a hundred-fold more effective than a printed notice, and is likely to become a permanent feature of campaign work in which the necessity for getting the voters aroused and inducing them to go to the polls is a prime factor. In the large cities political managers--the men who run the campaign machinery--make an extensive use of the mails and printed matter in interesting the voters and persuading them to go to the polls election day, which, after all, is the all-important thing, for if a man doesn't go to the ballot box it matters little whom he favors. Postage and printing bills form the chief expense in political campaigns. The Des Moines experiment may tend to change this somewhat. The telephone message "Don't forget to vote to-day" reaches the right spot. It also finds the man at the right time. He is not so likely to ignore such a warning uttered in the sweet voice of the girl at "Central" as he would a circular or postal card that is delivered by an over-burdened mail carrier--maybe hours too late.
    The telephone message on election day carries with it the "Do It Now" spirit, while the stereotyped printed notice usually finds a place unheeded in the waste-basket. The Des Moines plan is commended to all up-to-date political managers who want to reach the people in the right way and at the right time.