According to reports today, carriers are responsible for setting the number of devices that can be connected to the Mobile Hotspot feature that is part of iOS 4.3, which is rumored to be getting released today (via BoyGeniusReport). Apparently, the Personal Hotspot feature can support connection of up to five devices but, at the carriers request, it is limited to three devices.
It should be noted however, that if the new iOS version does appear today, this contradicts Apple’s own announcement suggesting that iOS 4.3 will be arriving on March 11th.
The connection of three devices via Wi-Fi tethering to an iOS device is one of the highly touted features of iOS 4.3. For AT&T owners, this means that they would have to subscribe to the $45 per month DataPro tariff allowing for 4GB of data (2GB of regular data and 2GB of tethered data). Verizon will apparently allow five devices to connect to their Wi-Fi Mobile Hotspot tethering option.
It is not clear why AT&T would be limiting the number of devices connected to one 3G connection especially given the fact that they place download limits on the data plans that they offer. It does leave them at somewhat of a disadvantage compared to Verizon in this regard but, to be honest, three devices sharing one 3G connection is plenty.