We have all been in situations when we get unwanted calls from telemarketers, unwanted friends, and strangers dialing the wrong number. Unfortunately, the iPhone does not have an ability to block unwanted numbers.
For those with GoogleVoice it's not an issue, since you can give your GV number to everybody and then block unwanted calls at will.
For everybody else, the simplest solution is to assign a silent ringtone to unwanted numbers. (Keep in mind that if you have vibration enabled, your phone will still vibrate.)
We took the liberty to create such a ringtone for you to download.
1. Download the ringtone from here.
2. For organization purposes, put it into your iPhone Ringtone directory.
3. Open the ringtone file using iTunes.
4. Sync your iPhone, making sure that the new ringtone is selected for the sync.