How to block a number on a iPhone 4S?

I can't find any type of way to block the number!

To block a number, check you are on one of these firmware's:

7.0
7.0.1
7.0.2
7.0.3
7.0.4

If you don't know what your running goto
Settings>general>about

If you are not on one of these firmwares then you MUST update to one of these.

So to block a number:

1. Goto your call history

2. When you see the number you want to block, press the i button.

3. Then press block this caller

Then your done!

There may be times when you need to make a call but don't want your identity or phone number to show up on the caller ID of the person you're calling. There's an option on the iPhone to be able to easily turn off the caller ID and for your number to show up only as a "Blocked" number when making calls. Here are some easy steps to turn off the caller ID option.
You can learn How to Block Your Number on the iPhone reading the following article

Ask the provider