Yes, pretty much. If enough people call to object then the prospect of losing the next election becomes real; they figure that if people are motivated enough to call then they might just be motivated enough to vote. That more than anything is what motivates politicians.
Faxes are actually the most noticeable and effective tactic.
Unfortunately I can't find a source for this but I saw someone saying recently (and it makes sense) that a lot of congress fax numbers just convert the fax to an email message rather than physically printing it out.
What's a fax? ;-)
Seriously though, how do you know this?
It's not correct. It's easy to ignore faxes, and throw them away by the bucket-full without ever reading them. A phone call requires spending some low level staffer's time to listen to you. Getting inundated day-in, day-out by callers, all on one side of an issue, does have some effect on a congressperson's staff, and sometimes, the congressperson's actions.
Is the goal to DDOS these offices with phone calls in hopes these politicians will rile together and pass a law?