Once I sense the silence is coming, I just wrap the conversation up and end it. It's no big deal if I'm talking to another guy on the phone, but if it's a girl I'll just say I have to go or something lame. I don't think you're going to hurt anyones feelings if you want to put the phone down since you don't want to get stuck in a one way conversation. Besides you can use it as leverage to meet up in person if they really want to talk to you.