@cstross The Telcos _really_ need to do something about VoIP and "offshore" calls.
1) Tag "International" calls as just that (this used to happen).
2) Tag VoIP calls as VoIP if they're external to your network (if BT, not 21CN or UK businesses, etc.)
3) Set up a reporting method and _DO_ something about the rogue VoIP providers. Exchanges are all computers now and have billing systems, so calls are trackable to the originating telco. If they're supporting abuse, block them.