Grandfathered Simple Choice

Actually after I last posted to this thread, I called customer service later at night and was able to find a TMo supervisor based overseas who was able to find the right plan codes and add them manually!! (In other words, they were able to allow me to add an additional line for the same fee as our current lines on our Grandfathered plan.) He said that for the agents, the service codes are found under plan options and features, and that the old legacy tool they use (Samsung) can't do it. I'm not sure exactly what that all means, but perhaps if you tell a customer rep that will help move you in the right direction!