This might annoy a few people but hey, you can't please everyone ;)
I had this conversation with a fellow instructor about answering mobile phone whilst teaching. I don't normally do it and most people know that they have to phone me after 7pm if they need to speak to me. If I am having a lesson myself I am not keen on my trainer chatting away on their mobile either.
Having said that, there are a few numbers stored on my phone that I will always pick a call from; that includes Ricky, my family and a few friends. This does not mean I will get into lengthy conversations about everything, nothing and the purpose of human kind! If the person on the other side of the phone isn't just catching their last breath my standard response will probably be something along the lines of 'I'm teaching now, can I call you in so-and-so minutes'.
Some clients don't like any of that considering it an invasion into the time they paid for...
Fellow instructor told me I should have my phone switched off during lessons...well, I am afraid I am not going to do so.
Funnily enough, I am more likely not to have my phone with me when I am schooling/riding and I might be so focused on the horse that I won't even hear my mobile ringing ;)
Sometimes I might leave it in a 'safe place' and have no idea where that was!
Either way, I always return the calls ;) If you called and didn't hear back from me you probably have your number witheld!
Anybody who rides with me knows very well they won't loose anything because of me answering the phone...You cannot escape from hard work and constant improvement on my lessons ;)