I haven't had any problems with the system recognizing my voice commands. However, the system didn't recognize my confirmation number on one attempt, and the agent to whom I was transferred handled my upgrade request (which cleared this morning ).

On another occasion, I wanted to upgrade a one-way trip with miles. There was no option available for upgrading with miles, so when the system asked if I wanted to upgrade with 500-mile coupons or a confirmed upgrade, I said "neither" and was transferred to an agent. Again, the agent took care of the request for me.