He's hazy and waking up from a lot of drinking when he gets the call. He recognizes the voice and just mumbles sounds of agreement to the beginning. However, that introduction wakes him full up.

"Other Balthazar?" Beelzebub glances around wide eyed wondering if Lucifer knows. "Wait... Are you fucking with me? Lucifer's probably there laughing after that booze he gave me last night."