Take movies for starters. Movies have to make choices. If the camera is with one speaker, can you hear the other side of the phone conversation? If not, it can be pretty tough to figure out what's going on based on just half of the conversation. If so, it can seem cheesy or just be downright confusing. Moviemakers might try a split-screen presentation of both speakers, but that makes things completely unrealistic. In real life, you'd only be observing one half of the conversation. On the other hand, moviemakers might only let you hear one side of the conversation, but leave their audience feeling frustrated and out of the loop.
After the jump: examples of proper phone usage in fiction.