I recognize Badspots lust for money, but maybe he could take one for the team and IP ban them?
Proxies, cell phone data plans, and the dwindling number of ipv4 addresses causing isps to recycle more rapidly has caused IP bans to be useless. I'd rather have them just give me the money than spend money on one of these circumvention methods.
Side note: with a little bit of effort virtually all proxies could be blocked. The same proxy lists available to jerks are available to me, and they could be mined for hostnames and ips. It's never been enough of an issue for me to go forward with it.
Re: prank calls
Leave the phone of the hook for a day or so, most jerks get bored by that point. If the problem persists and you know who is doing it, you can actually contact the police because prank calling is IRL illegal. Source: My mom is was a teacher, this stuff happened to us once every year or so.