Thank you for this question about phone courtesy.
In fact this is considered rude in most business circles. The only acceptable way to take a call such as this, in terms of courtesies, is to ask permission, and then only if it is an important expected phone call.
In my business circles, we inform persons up front, that we have time to talk, but that I may be interrupted by an important income call; then ask "is it ok if I take that call momentarily". In most cases we get told it is ok.
In so doing, it is understood, that we do not have several such important calls.
it is expected that if we have agreed to talk no the phone, that those obstacles are cleared right away, or that we respect the person by not taking the call. The caller can always leave a message if your sister does not pick up. And she can return the call later when you are done.
However, such courtesies are forgotten when people are in personal circumstances.
It is rude and inconsiderate. When she is in communication with you, you deserve each other's undivided attention. It is only respectful.
In my circles, we do not even have a cell phone turned on during dinner, in private clubs, or on dates. If we need it turned on during a date because of that important call we expect, we clear it with each other, and do not answer the phone unless that one call comes in.
What your sister is doing is considered inconsiderate and rude. It is not being respectful of you and your needs.
Thank you for confirming my thoughts on telephone courtesey. I should have claified that our calls are all long distance. I have been left on the line sometimes as long as 5 minutes while she converses with the new caller. I don't know how to tell her this is RUDE as she will take offense. Any suggestions.
I do not know your sister. But sometimes honesty is the best policy.
My recommendation is to simply wait until there is no call, and then in a quiet moment, ask her if she would do you a favor and not take calls while you are talking on the phone. let her know that it is very disrupting and you really want to savor the time you have with her on the phone. That you consider that (our) special time.
If she does not respect that then there is phase two.
When she interrupts the next time, simple sign off. when she comes back on she will find you gone. When she does reconnect and ask about it you can say something like: Sis, I really enjoyed being on the phone with you, but I though we were done because you left the call.
A few times of that, and she will get the message.
The main thing, is sometimes you have to stand up for yourself, and be true to yourself. You are not responsible for your sister's feelings. She should respect and value you. AND you are responsible for your own feelings. You do not have to feel guilty about this. Just do it with politeness, respect and tactfulness.