Yes, as long as they as they are not for marketing purposes!
It is important to remember that sending mass messages over SMS is highly regulated, and there are legal restrictions around sending text messages for marketing purposes - for instance, marketing messages must be sent using a short code rather than a 10 digit number, which Textline does not offer. Contacts will also always need to “opt in” before these texts can be sent.
It is also possible to use a short code with Textline. You can read a little more about how to do that here.
Watch the video tutorial on Using Announcements here.