That's because the PET is also a device that can be used to give input in battle and select relevant programs. It's designed to be compatible with as many electronic systems as possible.

It's also got a projector, so holographic keyboard input is possible. [ There's also attachments for the PET that make typing easier. ]

This is a housing for a netnavi, an AI. That's why it hasn't got all the features that you might see on cellphones - the netnavi inside handles some of those tasks.