Some cell phone carriers will let you block unwanted callers. I have verizon and I'm able to block calls and text. The only way that I'm able to do that is logging in online and doint it from there.
Some Panasonic phones (the ones that say "Call Block") will let you block out of area numbers. Once they're blocked, the phone rings once on your end, and the caller gets a busy signal. We got ours from Amazon for about $25 and plugged it in as an extra phone just to block numbers.