IPhone – Port blocking on iPhone 6

A new feature of iOS 7 is call blocking and it allows the device to block calls apart from the previous solutions that involved jailbreaking or having the carrier block calls for you.

Go to recent calls within the phone app. Tap on the "i" to the far right of the number you wish to block. On this info page, scroll down. At the bottom of the page, tap "Block this Caller". Confirm on the warning message.

From the settings app, use iMessage and FaceTime preferences to manage the block list.

This list blocks calls, messages and FaceTime calls (audio and video) from that contact. Combined with a blocked contact as Loïc Wolff has proposed, you have a neat solution for dispatching unwanted calls on an ongoing basis.

OS X actually has (at least) 3 firewalls. Since you've turned off the application firewall (in System Preferences -> Security & Privacy -> Firewall) and checked the Berkeley packet filter (pfctl -sa), I'm guessing it's the old ipfw that's doing the blocking. You can check with sudo ipfw show -- that'll list the active rules, along with counts of how many packets and bytes each one has applied to:

$ sudo ipfw show
01000 19228642 23229993542 allow ip from any to any via lo0
01010        0           0 deny ip from any to 127.0.0.0/8
[etc...]
65534    23505     3467352 deny ip from any to any
65535        0           0 allow ip from any to any

If your listing only shows rule #65535 (the allow rule at the end), my guess is wrong and you have to look elsewhere. If it does show other rules, you probably have a third-party firewall config program installed somewhere (I don't think the Apple-supplied ipfw config software is still there in 10.8); take a look in /Library/StartupItems and /Library/LaunchDaemons for things that might be relevant.