It never hurts to make a small campaign contribution along with voicing your concern, or mention a past donation. Forming your own local donation pool or interest group, even if it's small, is another way to do it. I'm pretty sure if the average HN member formed a small group with local co-workers and agreed to donate just 1 hours worth of wages, it would be taken seriously.

Unless things have changed a lot since I was there, the real advantage of calling a congressional office is that you're entered in a database faster with your associated issue. It's not like your congressperson answers the phones. That's what the interns and staff assistants do, who hold zero influence.

Be patient with the person taking your call. Many people who call don't even do it right. They contact someone who isn't their senator or representative, which gets ignored. They just say "Don't vote for X!" and hang up without providing contact information.

Also, if you don't vote, many representatives have a database from their board of elections saying which registered voters actually showed up to vote. You're put on the bottom of the stack.