The characters are sharing their stories about Cab 804, but when Tom Selleck gets in the cab, the number on the door is 264.
In Elaine's fantasy, Louis couldn't possibly listen in on Elaine and Mike's conversation. Elaine has to press the PTT (Push To Talk) button on the handset for the radio to transmit and for Louis to hear them. What's more, if the button were inadvertently pressed and held, the radio would be in transmit mode and they wouldn't be able to hear Louis.
Guest star Tom Selleck introduces himself as Mike Beldon, but when he leans over the seat, the "TWS" monogram on his cuff is clearly visible.
Cab 804's numbers are obviously just a sticker placed on the body, and not painted on. The numbers also change color, from red to black.