I think this could effectively amount to eventually blocking the whole space, but in my universe that would probably be a good thing :-). It’s possible that a “backdoor” block like this was more politically palatable than overtly disallowing all telemarketing.

I guess the real issue is how much telemarketers care; if it’s really worth something to them, they could presumably encourage (or even pay) telcos to ensure that recycled numbers get reported. If, on the other hand, they’re all just moving on to on-line spamming…

I can see why scrubbing phone numbers after five years might be useful, since people do not generally call the do-not-call maintenance line and remove their number when they stop using a particular number. Having an address set that non-decreasingly increases towards holding its entire address space seems somewhat pointless to me.

Better would be to simply acknowledge this effect and ban unsolicited telephone advertisements altogether. That, or have the DNC list be informed by the telcos when a number gets recycled to another user.