United isn't the only airline interested in air taxis and the possibilities they might bring. American Airlines and Boeing are also investing heavily in the concept. According to The Wall Street Journal, Boeing is throwing $450 million into a joint venture with Google co-founder Larry Page. If the Boeing/Page effort bears fruit, you could be whizzing around a city in a self-flying air taxi within the next few years. American Airlines has chosen to back Vertical Aerospace, a similar company to Archer Aviation, to the tune of $25 million.