Of course I use various procedures to ensure that the system works, including procedures to restore service in case of temporary failure. In the unlikely event that there is a problem with a line or piece of equipment, it is relatively simple to find a replacement. The main point, though, is that telephones work most of the time and are dependable. Fourth, telephones are flexible. As I just indicated, I can teach a course from almost anywhere, to students anywhere, and I can bring in resources from anywhere to enhance this instruction.
Audio teaching needs no special technical support.
Especially important, after the class they can immediately return to work, taking with them the learning from the class. A good instructor will encourage students to bring work problems from the workplace to the learning program. The medium is also flexible with regard to time. During a class session, I can be confident in telling my distant groups to hang up the phone and disconnect for a period of discussion or other group activity and then to re-dial. I know the audio system will bring everyone back together with a minimum of fuss.