Yes, it's a true fact that you can pay money for the privilege of extending the cell phone provider's network, while also paying the backhaul the cell phone company's traffic over your internet link, while also paying the cell phone for their "service" that you have to personally install and operate. I have no idea why people think this is an acceptable scenario.
The providers apparently assume that you're already paying for "unlimited" internet.
Also, these access points pair with your device and don't provide bandwidth to other random devices, so at least you're not providing free backhaul for random passersby.
I got one of these for my apartment, worked great for 2 years but I could never add other people's numbers to it like advertised. It just paired with my phone and only used my internet connection for SMS/calls as long as I had wifi on (it would use my internet connection for 3g data but that would kill my battery and be silly to use with a phone that has wifi, it would also count against your quota if you had a limited plan).
There are other ones which are just a simple amplifier, not a whole base station. There's one antennae on the outside, another smaller one on the inside, and whatever signal it picks up one one antennae, it retransmits on the other with more power. Obviously the antennaes are directional so you don't get feedback, and there might be some more complicated filtering too.
It's a solution to a problem, that he faces. I understand that it makes no sense, but sometimes you have to do things that make no sense or switch carriers.