Q: blacklist

Only your carrier can do this, so contact them to see if they offer call/sms blocking.

Apple's iOS does not have a built-in feature to block a phone number, but there are other solutions.

1. Your carrier might be able to block individual numbers. AT&T has an optional feature called Smart Limits for Wireless that runs $4.99 per month. One of the many functions is the capability to block up to 30 numbers from calling or texting your iPhone.

Verizon Wireless offers Spam Control for no additional charge. This feature can be found under My Services when logged into your account, and blocks up to 5 numbers from calling or texting.

2. Make sure you've registered your iPhone number with the National Do Not Call Registry. This will not stop texts, but it will require most telemarketers to stop calling your line within 31 days. Complaints can also be filed using the same website, and phone number registrations with the service never expire.

3. Assign a silent ringtone to the numbers you don't want to answer. This stops calls from bothering you, but texts will still sound an alert. The iPhone doesn't come with a silent ringtone by default, but you can install and configure a silent ringtone with these instructions.

4. Another calling only solution are services such as TrapCall, which has plans starting at $3.95 per month. No iPhone app installation is required, and once you're signed up TrapCall will unmask blocked caller IDs and blacklist unwanted callers. More expensive plans can be purchased that offer more in-depth functions.

I believe this is now possable, blacklisting a number that is. But only if you have IOS7 installed on your iphone. A friend showed the option at the bottom of the edit contact screen I think.

hope this helps!

Fredy

iOS 7: Understanding call and message blocking:  http://support.apple.com/kb/HT5845

This is not like a cellular carrier block, more like a ignore calls and texts from a specific contact.  Text messages will not appear and calls will go to voicemail without the iPhone owner ever seeing a message or hearing a ringtone.  As mentioned above, a true block from the carrier costs money.  The one in iOS 7 is free.

Freddy is right. If you upgrade to iOS 7 you can block messages, calls and FaceTime calls.

Settings > Phone > Blocked

Or

Settings > Messages > Blocked

Or

Settings > FaceTime > Blocked

If you block a number in any of these locations it is blocked from all. The blocked list is global and applies to all three apps.