"I didn't know it was you."
"I didn't know you had called."
"I didn't get the message."
A couple of decades ago, these were all pretty good excuses for not taking or returning a phone call. Now? Not so much.
Thanks to caller ID and voice mail, there's very little excuse for not knowing that someone has called. Sure, about 1 out of a 1000 calls goes into a strange phone-void where the call isn't completed and the recipient has no idea a call came in to begin with... but that's pretty uncommon. And if I call a second time, it's about 1 in a million that you don't have a record of either call coming in.
Sometimes I don't even leave a message, because most phones will indicate if you've missed a call and will display the number for that missed call. Odds are, if I want to to talk to you, you already know me as soon as you see that number. If I don't think you do, I'll leave a message.
I have my phone number blocked on my iPhone so that it doesn't show up every time I place a call, but I also have programmed in *82 in front of the numbers of all the people programmed into my iPhone, so that it overrides that number-block and shows you who I am (or at least my number). I am well aware that you might not be able to take the call when I place it, but there's no reason in the world you can't call me back later on (other than unwillingness).
Even worse is the person who accidentally accepts the call while trying to screen it. I can hear him/her talking to someone else, so I know that (a) the call went through, (b) the recipient has looked at the phone and can see the number, and (c) he/she knows I called. If I can hear ten or fifteen seconds of your conversation and then you never bother to call me back, that's about as clear an "I don't want to talk to you" message as I can get.
The only thing more stark than that is the caller who, while screening missed calls, accidentally returns my call and doesn't know it. Then I not only know that you saw that I had called, but I sometimes hear you talking about it. "It was Cliff. He wanted to know how we were doing..." From there, the conversation wanders. But y'know what? Saying "I didn't know you called" really won't work then--nor will it be very convincing when you tell me "I was too busy and forgot to call you back," because I heard you doing nothing in particular while you were checking your missed calls.
When Dad was alive, there were people who he just didn't call. "Why should I?" he asked me when I suggested he give them another call. "They could just return any of the last two dozen calls I've made if they wanted to talk to me." And y'know, he was right...
So I'm taking a hint now, the same way Dad did. If I call you two or three times and you don't take my call and you don't call me back, then I will finally realize that you're not interested in talking to me. So I'll wait and see if you want to call me on your own schedule sometimes. If not, then I'm going to be okay with it.
'Cause you know, if you really didn't feel like taking or returning my calls, I guess we weren't on good enough terms that I needed to talk to you anyway...