You can do so through your device’s phone settings.
Detailed information on the respective mobile devices can be found by clicking on the following link: Device instructions from manufacturer
Please note that the function «Hide number» is currently not supported on certain Apple devices or iPhones.
We were able to pinpoint the cause of the issue and have discovered that the problem of the missing «Hide number» feature is linked to certain Apple iPhones and is not related to the swype SIM card. We are working together with Apple to fix this problem as fast as possible.
In the meantime, you can enter the number you want to call as follows: enter #31#PHONE NUMBER and then press the call button. Your call will be displayed as «Anonymous» to the recipient.