If your congressman is a Republican, then calling them and asking them to vote a certain way may have an impact.
If your congressman is a RAT, like mine is (Zoe Lofgren), then your phone call has no impact, as RATs are not independent thinkers. They vote how every other RAT votes. They vote how they're told to vote.
You got that right. I received the call to action from my fellow fairtaxmichiganders and they were kind enough to provide me with Carl Levin's contact information. I don't think I'll waste my time.