One of the regulations of using the ISM bands is that you must not cause interference with other devices. In the case of wifi, this is achieved using both colli

One of the regulations of using the ISM bands is that you must not cause interference with other devices. In the case of wifi, this is achieved using both collision detection, and noise immune modulation methods. Most of these mobile hotspots are going to be limited by the cell connectivity, not the wifi speed, so it would be pretty easy for multiple APs to exist on the same channel.