Called 1K line earlier today, hit 2 and was given the voice response system. I went through the whole process just trying to change seat assignments. It finally transferred me to an agent who answered IIRC "United shop for flights" or something like that instead of the 1k-specific greeting.

Called back for something else a little later, pressed 2 and went right to an agent with the usual 1k greeting.

Maybe if there's not an available agent immediately it forwards you to the voice recognition system instead of placing you in a queue for an agent?