Voice mail. Never answer your phone if you have voice mail. People don't call you just because they want to give you something for nothing-- they call because they want YOU to do work for THEM. That's the way to live. Screen all your calls through voice mail.
If somebody leaves a voice mail message for you and it sounds like impending work, respond during lunch hour. That way, you're hardworking and conscientious even though you're being a devious weasel. If you diligently employ the method of screening incoming calls and then returning calls when nobody is there, this will greatly increase the odds that they will give up or look for a solution that doesn't involve you.
The sweetest voice mail message you can ever hear is "Ignore my last message. I took care of it." If your voice mailbox has a limit on the number of messages it can hold, make sure you reach that limit frequently. One way to do that is to never erase any incoming messages. If that takes too long, send yourself a few messages.
Your callers will hear a recorded message that says, "Sorry, this mailbox is full"--a sure sign that you are a hardworking employee in high demand.