Absolutely. Telephones are an enormous nuisance for exactly these reasons. I have found Cyanogenmod's built in call blocking to be essential; I have it set so

Absolutely. Telephones are an enormous nuisance for exactly these reasons. I have found Cyanogenmod's built in call blocking to be essential; I have it set so all calls from withheld numbers and all that are not in my contacts are blocked. I let texts through, though they could also be blocked. If I expect anyone to call me who can't be persuaded to use email instead (e.g. a tradesman or shopkeeper) then I add their number to my contacts or ask them to call at a particular time when the blocking can be temporarily turned off. Only once has this latter tactic resulted in a spam caller getting through.