An increasing number of doctors are asking patients to pay an annual fee to gain access to their examining rooms. The trend is on the uptick nationally, particularly among experienced doctors frustrated by what many see as an insurance system that's reducing doctors' pay, coming up with new pay-for-performance rules, or pushing them to see more patients to lower costs. But some healthcare analysts warn of a widening gap between the haves and have-nots. Paul Ginsburg, president of the Center for Studying Health System Change in Washington, D.C., said the new business models could create a class system in medicine.