Short codes have been the traditional choice for commercial uses of text messaging. They were the first method that was approved by carriers. Recently there has been an advance in technology that allows us to text-enable any standard toll-free number (abbreviated as "TFN"). There are a lot of advantages with a TFN and one minor quirk that should be understood before implementing one for your utility, court or enterprise.
It's all about how to opt-out:
A better approach, and the one that we advocate, is using QUIT instead of STOP. This processes the opt-out in the same manner that we are all accustomed to. The message is NOT recognized by the network and gets passed to us normally. We opt-out the subscriber and no more messages are attempted to that number. When the user wants to opt back in they do not have to send UNSTOP first. They simply send the keyword and they will be opted back in.
It's a small difference - just using QUIT instead of STOP - but it makes things cleaner and more definitive.
What's the bottom line?
If you are using a text-enabled toll-free number tell your customers to reply QUIT instead of STOP to opt-out.