What I also use is google voice. I only give out my google voice number and it saved me a lot of time not having to answer calls. Google voice translates phone messages to text and I can just look at the message and I can block it within the google voice app.
pre-paid pones require at lease $10 / month to renew the service but you don't have to use any of your balance. I seldom use mine - I switched off the airplane mode when I expected important incoming calls on that day only and if used, $2 / day covers everything unlimited.