What about caller ID?
My father does a show on an a.m. station in Newport, and there have been a number of times where he's had me fill in for him because he was heading out of town. He does a music program that doesn't take calls over the air, but there is a long-running afternoon call-in program called Open Forum and they get some shitty callers from time to time. One time when I was subbing (probably like 10 years ago now) I noticed a list of phone numbers sitting by the phone in the control room, so I asked the engineer about it. He told me that the station "finally" was convinced to invest in caller ID so they could weed out at least some of the frequent conversation killers. The list, which at the time had about two dozen numbers on it, is pretty hilarious, i.e.:
8-5555 - Flo Schmoe
6-1234 - Drunk
5-1111 - Betty Something (drunk)
4-2222 - Senile, Rambler
5-3333 - Retarded
3-5552 - Joe Shmoe
5-1111 - Irish guy
5-9999 - Crazy
5-8888 - Right wing nut
4-9999 - Lawyer
4-8877 - Drunk?
etc.
With cell phones and ID blockers, I'm sure you can't catch them all, but it might be a small step in weeding out some of the riff raff.
I know I don't want to see the show go down because of a few douchebags.