Phone Etiquette

Two days in a row this has happened to me. I was on the phone yesterday with a student and he told me that he had a few minutes to talk. We started our conversation and all of a sudden I hear a different voice in the background. I guess the gentleman I was on the phone with had his blue tooth in and the other guy didn't realize he was actually on the phone. Things could have gone very differently if the man on the phone with me would have let the other gentleman know that he was on the phone but instead he proceeded to have a conversation with the other guy and ignore/forgot about me. They started talking about which barber to go to and both men started using some pretty serious profanity. What made things worse on my end is that my manager was sitting with me, monitoring the call, and seemed to be much more offended than I was at what was going on. After about five minutes, yep that long, my student got back on with me and without an apology started back into our conversation as though nothing had happened. I shrugged it off and didn't think too much of it but then this morning I was on the phone with another student and she did the same thing to me. I understand that I may not always be the most present person when I am on the phone, usually due to multi-tasking, but I have never attempted to hold two conversations at the same time or completely neglected one conversation on the phone to hold a different conversation with someone else while leaving the person on the phone hanging. The issue I take with this is not that it happened to me but that it happened at all. Am I the only one with this issue or is something that others have seen as well?