My observation is that most of us automatically send the type of communication we prefer to receive. But it’s probably not a good idea to send text messages to clients who resent paying extra on their phone bill to receive them. It’s also probably not so good to send e-mail to clients who don’t really use e-mail and who would prefer an old-fashioned telephone or face-to-face conversation.
There are many different communication channels these days and most of us have our favorites. The same is true for your clients. So when you first meet a new client and you’re getting their contact information, ask them how they prefer to communicate and honor their preferences.