There is a little work around that will allow you to do this. You can create a Group/Queue for all the users that you want to text, and then send the text to the group.
However one limitation to this is that when any of those users reply it does not maintain the group format and all reply's become 1-1 conversations. But if you are just needing this to broadcast company announcements or something like that, then it will probably work fine.
Group Texting needs to be fixed. I have to reply to the group but keep getting "Your phone number used in this thread is no longer available.". I choose my number, and then it states I have no valid numbers (null). You should just be able to reply to a group message. If you know of a workaround, please let me know.