Have you ever walked into a dark room and said "Computer: Lights" to yourself? One of the most iconic parts of Star Trek, as well as other sci-fi, is the characters verbally issuing commands to their computer/robot/android then listening to their response. However, on the bridge of the Enterprise the viewer rarely saw the crew talking with the computer but rather busily typing commands into their stations. This is easy to understand as it would be hard for the captain to command the ship or talk to someone through the view screen if he was surrounded by people talking to the computer, much like the experience one would have on a train if everyone around them was asking questions to their smartphones.
This was a problem that quickly developed with cell phones as people becoming annoyed when someone in earshot was talking on their phone. It has become its own category of bad behavior and has caused cell phone use to be discouraged or banned in certain situations. In addition, multiple people attempting to talk on the phone together is also disruptive, either to the other callers and to the conversation in general. To solve this people turning to a more private, silent form of communication that still involves words: text messaging.
In addition to the ability to conduct private conversations in public, communicating with written text allows for greater accuracy and a record of what was said. If someone want to know an address it is much better to be able to repeatedly refer to the original text message then to hear it once or maybe refer to something that had to be transcribed from what the recipient thinks they heard. This is especially true if there is background noise or they are in a crowd, something that is common when using a smartphone.
Despite the fact that the assistants are responding to commands that can be easily written, many insist or promote the user having to speak the command. In a restaurant why does someone have to choose between speaking "Add an appointment tomorrow at two PM" and possibly disturbing the other customers or manually entering the appointment? They should be able to text the assistant the same command, much like they would with a human assistant and have the task completed with any responses texted back.
While it may not be as iconic or fun as saying "Computer: What is my location?", the ability to text "What is my location" to a smartphone assistant is far more useful since it integrates much better into the user's daily life.
