There's big money in the reverse phone sector if you have the right connections. I don't understand why this is a bad idea...
I was going to say something similar... There are many ways to make money and be successful that are not in phase with other folks ideals. Just because an idea has already been tried doesn’t one mean one won't succeed.
The assumption the op has taken that they are right and the client is wrong is interesting.
If the client is paying for the product - give them a good product.