I haven't heard of UberPop in the US: a quick google says it sounds like a more open version of UberX, so it would also be illegal: the sticking point is drivers without a professional license/commercial insurance taking money from people for rides. In the US the version of Uber that uses professional drivers is technically called Uber Black: in my experience when people say "Uber" they mean UberX (because it's cheaper and so more popular).
