[nkurz]

This process seems ripe for abuse. Phone calls do not necessarily come from the geographic area they appear to, and there likely aren't any legal consequences for lying about zip code.

How can this be both the most effective way to influence a politician, and at the same time not be subverted to the point that such feedback cannot be trusted? Are there other checks that are less obvious?

If what you say is true, I'd have to believe that lobbying groups are already abusing this, either by posing as people they are not, paying people to pose, or by paying actual constituents to express concerns on their behalf.

[rdhyee]

I've wondered about this question myself. Wondering whether a financially well-resourced group would just use money to get access as an easier and more efficient approach to influence of a member of Congress. That to simulate an avalanche of calls from concerned citizens by paying people to call is a less financially efficient method to get influence. (I'm just speculating.)

[nkurz]

That's plausible, but I think it would mean that phone calls don't actually have much influence if someone with money is influencing the politician in the other direction. I'm willing to believe that phone calls actually don't have much influence, but I keep hearing from former staffers that they are influential. Maybe they say this because it influences their recommendations to the politician (which may or may not be heeded), but this would still leave the system open to abuse.