Is there any way or an app for iPhone to block calls from people?

I keep getting spam calls from telemarketers, is there any way at all to block their calls? Calling 7 days a week gets terribly annoying.

You can't block certain callers but for telemarketers you can put your number in the National Do Not Call Registry (follow the instructions here):

If you know the exact number of these spam telemarketers then blocking their calls is quite easy. Just type 'block calls' or 'call blocker', in the app store and voilà! With any app on the list you can block the calls. If you don't know the number then I'm afraid you have to bear the calls of the telemarketers.

Dont ever put your number in a website, if its a legitimate site like a well known company your ordered from then I think thats fine, but otherwise never enter it elsewhere.