Techinically, SMS will tell you they are not locking anyone out.  They are simply requiring the current Game Dev version (and from what I can tell future versions of Poser) to have internet access so that they can connect to the SMS server for verification once every 90 days if the system it is installed on has a continuous internet connection.  If it does not, either they user must connect and allow the app to go through the verification process once every 180 days or the app will deactivate.

Nitpicking, I know but that's pretty much the explanation you will be given.