USSD Codes (Inner Dialing Codes): What They Are and How They Work

USSD (Unstructured Supplementary Service Data) — aka "quick codes," "feature codes," "star-hash codes" — are real-time, session-based strings you dial to talk directly to your mobile network. No app, no data, no SMS store-and-forward.

How They Work

1. Dial: *123# (example).
2. Phone sends USSD request to network via signaling channel (SS7/MAP).
3. Network app (HLR, VLR, IN, USSD gateway) processes.
4. Response pops on screen instantly (max 182 chars).
5. Session can continue: menu → input → sub-menu → result.

Common Uses

Key Traits

• Instant: No SMS delay.
• Interactive: Menus, prompts, multi-step.
• No store: Not in call log or SMS inbox.
• Network-specific: Codes differ by carrier/country. Check your MNO's website.
• Potential cost: Some carriers charge per session (rare now).

Security Note

USSD can trigger actions (factory reset, call forward, USSD-based payments). Don't dial random codes from untrusted sources. Malicious USSD (e.g., *2767*3855# = Samsung factory reset) exists.

USSD is the CLI of mobile networks — powerful, invisible, and still everywhere.