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USSD on a Sony Ericsson mobile phone (2005). Unstructured Supplementary Service Data (USSD), sometimes referred to as "quick codes" or "feature codes", is a communications protocol used by GSM cellular telephones to communicate with the mobile network operator's computers.
Fixed Dialing Number (FDN) is a service mode of a GSM mobile phone's SIM card. [1] Numbers are added to the FDN list, and when activated, FDN restricts outgoing calls to only those numbers listed, or to numbers with certain prefixes. [1] A notable exception is that emergency calls to 000, 112, 911, 999 and the like are exempt. [2]
ETSI and 3rd Generation Partnership Project (3GPP) standards, such as GSM and LTE, define supplementary service codes that make it possible to query and set certain service parameters (e.g., call forwarding) directly from mobile devices.
The Type Allocation Code (TAC) is the initial eight-digit portion of the 15-digit IMEI and 16-digit IMEISV codes used to uniquely identify wireless devices. The Type Allocation Code identifies a particular model (and often revision) of wireless telephone for use on a GSM , UMTS , LTE , 5G NR , iDEN , Iridium or other IMEI-employing wireless ...
An intermediary machine or process rejected the call attempt. [25] This contrasts with the 607 (Unwanted) SIP response code in which a human, the called party, rejected the call. The intermediary rejecting the call should include a Call-Info header with "purpose" value "jwscard", with the jCard [26] with contact details. The calling party can ...
By connecting a test telephone set, a technician calls the local telephone number of the automatic number announcement service. This call is connected to equipment at the central office that uses automatic equipment to announce the telephone number of the line calling in. The main purpose of this system is to allow telephone company technicians ...
Depending on the carrier which the phone is locked to, only some codes will work with the mobile phone. Most phones respond to the unlock codes ending in +1# or +7#, however some phones are configured to allow only one of the seven codes to work. The following is an example of a DCT4/DCT3 unlock code: # pw+931882753035021+7#
Call again, a form of automatic ring back, allows a caller, on reaching a busy signal, to hang up, dial a special code, and be called back automatically when the called number is no longer busy, usually with a limit of 30 minutes. Call return allows a customer to dial a code that identifies the last incoming call. On some types of central ...