Bad advice. The phone only allows xyz decibels, you hurt your ears and not theirs. As for blocking, better off buying your own device as you can block 1500#'s or more if it has area code blocking..
Do a search on call blocking devices and phones.If its a cell phone, there are free call blocking apps out there including trac & straight talk.
http://800notes.com/forum/ta-5d4e343675a5629/call-blocking-devices