So, you mean violate the AUP on your phone and push the costs for the people selling you the data plan upwards? sure, maybe that'd kinda work until the upstream noticed.
If you mean that it would have been cheaper to just give each homeless person their own phone +data plan... that might actually be a better idea, if you can find a cheap enough data plan/phones and you aren't supporting that many homeless people.
To go back to the restaurant example, you have to hand out a lot of soup before running a soup kitchen becomes cheaper than just handing out McDonald's "free item from the dollar menu" coupons.
That's a reasonable thing to consider, assuming that the quality is good enough.
You're still underestimating the man hours, equipment costs, and recurring nature of this endeavor. And this service is providing a needed connection to important information, contact with loved ones, and a safe source of entertainment. It is not comparable to the luxury service you grew up with.
I could provide wifi access to 10 people with only my cheap data bill + phone. It wouldn't be an ideal situation, but it would still be a better user experience than the dial-up internet I grew up with.