GSM Codes (often referred to as USSD codes or control codes) are short sequences of digits entered directly into your regular phone dialer to control carrier network functions.
They work worldwide across any mobile network and with virtually any device—completely without requiring an additional app, hidden settings menus, or an active internet connection.
Most commonly, these codes are used to quickly set up call forwarding. However, they also manage features like call waiting, caller ID blocking (CLIR), or retrieving internal device information (such as your IMEI number).
How to Use GSM Codes
The process is identical on both iOS and Android and takes only a few seconds:
- Open the standard Phone app on your smartphone.
- Enter the control code exactly as listed in our table (including all asterisks
*and hashes#). - Replace placeholders like
[Phone Number]with the actual target number (e.g., the number of your cover representative or your AI assistant). - Press the Call button (the green phone icon).
- Wait a brief moment for the confirmation message to appear on your display.
The Logic Behind the Codes
The codes follow a consistent structure that makes them easy to understand:
- Codes starting with
*or**activate a feature. - Codes starting with
#or##deactivate or delete a feature. - Codes starting with
*#check the current status of a setting.
Forwarding Unanswered Calls to an AI
The most valuable application for call forwarding in everyday business: Forward calls during a “Busy” signal or “No Answer” status directly to an intelligent assistant that reliably takes care of your customers.
An AI phone assistant from Hallodesk answers your calls, has a natural conversation with callers, answers questions about your business, and sends you an immediate summary via email or WhatsApp.
