In the US politicians take calls and written letters most seriously.

It's far, far too easy to tweet or facebook something. A passing emotion with no commitment. If someone writes a letter they have put a lot of effort in and are seriously involved in the issue. They might even do something as outdated as vote or talk to their neighbors.

That's the kind of behavior that is dangerous to a politician and gets noticed. So written letters and phone calls are the best way to get a politician's attention.