The animation is pretty nice, I like the style and the detail involved. The voice-acting is surprisingly effective, and the singing bit was really good. Your direction and writing were especially captivating, felt like a legitimate television cartoon.
Ambient music throughout would help the story, quiet scenes tend to rely on the dialogue and tension for interest which can be inherently lacking in a short movie, you might find some good ambience in the audio portal just to run with the theme of the dialogue. Also, more detailed backgrounds would compliment the detail of the foreground.
The artwork was great with the golden-age cartoonist effects like the mouth popping out of the phone, stuff you honestly never see in cartoons anymore, great stuff.