Attention: Not all telephony operators and the various countries use the same prefix to precede the number to make a call "anonymous" always try first that actually the prefix to work correctly. Some operators then use restrictions in this regard disabling the anonymous call restrictions which can be removed by calling your operator.

For example in India this service can be enabled but is disabled by default to legal restrictions. Even if you want to enable it then there are a lot of legal formalities from Telecom company to Police.

Sometimes for privacy matters we need to make calls without to see your phone number from who is on the other hand the application allows you to place a call anonymously in a fast and easy way to dial numbers with the dialer to the numbers in the Address Book or glued with the proper key so who will receive your call will not see your number but the words "Unknown" or "Confidential Number" or "private number".
The application is not resident in memory not consume the battery in your cell phone but to be able to call as anonymous must necessarily use the application.
To do this the application uses by default the prefix #31# but in the settings you can choose the most suitable to your operator and/or country.