NowClinic, which started in 2010 and has expanded into 22 states, is part of the explosion of Web- and telephone-based medical services that experts say are transforming the delivery of primary health care, giving consumers access to inexpensive, round-the-clock care for routine problems—often without having to leave home or work. Insurers such as United Healthcare, Aetna and Cigna, and large employers such as General Electric and Delta Air Lines are getting on board, pushing telemedicine as a way to make doctor "visits" cheaper and more easily available. Proponents also see it as an answer to a worsening doctor shortage. But some physician and consumer groups worry about the trend.