Come to think of it, it's weird how they didn't use cell phones. I guess they're not necessary in the world of HP.
Anyway, the comic has a simple set up and a simple, funny punchline. Very clever. The art is very simple, it delivers the message, but it's quite unrefined.
The coloring is quite bland and there's not really any shading done. You should also really work on hands, as these look very off and quite simple.