Pick it up...
...And then slam it down!
Do you mean to turn off the ringer so you don't have to listen to it? Some phones have an 'off' button for the ringer.
. I use PhoneTray Free.
Your telephone service provider should be able to provide you with a device known as a caller ID display, so you can decide whether or not to answer it. You can buy phones that include the function as well. Some service providers charge to allow you to see the number before you answer, others do not.Some of those devices also include an option to disconnect without answering.