"Type 121 to be connected or hold the line for endless cat facts at $5/min ... Did you know cats on average have just under 4 legs ..."
With the code being randomised and an actual pay service.
Someone in the UK did something like this, apparently, and made money.
Technically not, since "DTMF" is a proper noun referring to the overall encoding system, and is used as a adjective indicating that this particular tone is associated with that system. Compare "That farm raises KFC chickens. (That is, chickens intended for use by the resturant (chain) that calls itself "Kentucky Fried Chicken".)". Or "The left is what a MacOS window looks like, and the right is what a Windows window looks like.".
I use to use Google's call screening, and was foiled by this when I wanted to screw around with them by pressing buttons to speak canned messages. Google really needs to update that with a DTMF keypad.
For me the increase correlates to buying a car so I thought that the dealer was at fault but maybe it is just a coincidence.
I bought a vehicle from a major dealership, their paperwork had my name mispelled, but I didn't say anything or correct it.
I registered the vehicle with the state with the correct spelling of my name.
I started getting snailmail car warrenty spam with my mispelled name shortly after I bought the car.
The dealership said those spammers must have got it from the state's vehicle registry. I told them my name is mispelled on their paperwork and is mispelled exactly the same way on the spam, but is spelled correctly on the vehicle registration. *crickets*