TCR Registration Consent Forms

SMS is the same thing as a text message, isn't it? We communicate with clients via text messages for their convenience. They usually initiate the text message. We never use text messages for advertising, and we do not ask our clients permission to send text messages, since th client is almost always the one who initiates the exchange via text messages. In my opinion, this whole thing is pointless, but I am willing to do it up to a point. However, I really do not want to bother all my clients with a form to give me permission to respond to their text messages. Do you have any suggestion other than to forego this means of communication?