Phone etiquette: Are you obligated to answer the telephone?

My wife exhibits what, to me, to be a pathological need to answer the phone, almost as if she is under some social obligation to whatever person decided to dial her up at any given moment. She makes great efforts to get to the phone before voice mail kicks in, and gives me exasperated looks when I don’t move fast enough and miss a call. I, on the other hand, will ignore a ringing phone during dinner, will check the caller ID before answering and often will not answer if I don’t recognize the number (or at least the area code). This prevents me from talking to most telemarketers. Do you think that you are under a social obligation to answer the phone just because it rings? It seems silly to me, but on the other hand, if it were the front door, it would be awfully rude to hide until whoever was ringing the bell went away, so maybe I’m wrong.