I don't like to answer unexpected calls from anyone. It was different when the phone was the only instant communication medium... one hd more time to prepare for the content of a given call.
Now, it is always a distraction... my girlfriend frequently calls without warning in the middle of a text conversation, and i often don't answer because i'm not ready. It takes a far greater level of attention and commitment to talk on the phone than to participate in a text based conversation.
I think you have it right. No obligation to answer a call. Not answering just means that it's not a good time. Sadly a lot of people seem to think it is rude.
Now, it is always a distraction... my girlfriend frequently calls without warning in the middle of a text conversation, and i often don't answer because i'm not ready. It takes a far greater level of attention and commitment to talk on the phone than to participate in a text based conversation.