[the9to5]

Assuming you meant NYC, the problem for Hailo/Mytaxi/etc is that yellow cabs are only allowed to pickup street hails and can not be dispatched to you directly. So unless such regulations are loosened, these apps just won't work.

[untog]

There was/is an active pilot for "e-hailing", which Hailo participated in. I tried it - hailed a cab with the app and it drove up to meet me. However, people kept trying to get into it while I made my way over to it - people just aren't used to yellow cabs behaving that way.