HideMe helps you easily call any contact with a custom prefix for example to hide your caller id. You just select the contact from the contact list and make the call.
The code you entered (default is *67) will be dialed before the contact's number. For example in some countries if you prefix a number with *67 caller id is disabled for this call. Other functions include forwarding to that number etc. Actual codes depend on your carrier and country. A list of valid codes can be found in http://en.wikipedia.org/wiki/Caller_ID or your carrier website.