We've all heard the calls to action and gotten endless bulletins from mailing lists. Call your senator! Write to your senator and tell him or her you hate an upcoming bill! And one consistent question is, does it work?
All Senate offices are different. Some offices respond to mail from everyone who writes, whether the person writing is a constituent or not. Many offices get piles of mail everyday and can only afford to respond to constituents. Mail takes a long time to actually get to the office because it has to be taken off site to receive treatment. This became a priority when Hart Senate Office Building closed for a period of time when anthrax was found in mail. Staffers for former Senator Tom Daschle handled it calmly and carefully.
When the mail gets to the office, each office has a sorting process. Some of the more well-known senate offices need to cull out a lot of the stuff that's not worth replying to. Usually this includes people who are just ranting, non-constituents, and mass mailers. You may think that sending something en masse is going to emphasize to your Senator that a lot of people feel strongly about something, but it's actually much more like email spam. It's impersonal, doesn't show that the person has a stake in the issue, and it's frankly a little disrespectful not to have taken some of your own time to research and write personally to your Senator. Senators and staffers will listen to individuals with a respectful, logical argument that shows how the Senator can help personally. The response will most likely come from an LC, or a legislative correspondent specializing in certain issue areas, but it will reflect the position of the office. If there's some sort of constituent service that the office can provide in addition to replying, the office will likely do that as well.
How about calls? Again, each office has it's own policy. However, you can usually except calls to be written down and sent up the staff chain primarily on the House side of the Hill. This is because congressional districts are smaller, and the House works differently from the Senate. The House is focused on pleasing and responding to constituents, while Senators are elected to think in terms of both the national interest and the views of constituents. Senators may also be well-known, so individuals across the country may call in just to have their morning rant. Like the mail, you can stand out from the rest by making a fair and reasoned case.