Haven't been able to find much data on this by googling around, so maybe someone can tell me definitively? I remember reading that generating wifi from older android phones (like my Droid 1) is an ad hoc network, but a lot of newer phones are released intended to be used as a mobile hotspot, are these running in ad hoc mode as well?
Without knowing more about what exactly you're asking the answer is that practically speaking it doesn't matter. The differences between ad-hoc and infrastructure networks really only come into play when you're dealing with more than two nodes. I haven't tested it but I don't even know that iPhone or Android hotspots allow you to communicate with other clients connected to the hotspot. It's primary purpose is to serve internet and as a gesture to security in public places they might have simply just disabled client to client connections. Essentially, each connection becomes it's own two node network.