The three services offered by GSM systems are;

Telephone services

Bearer services

Supplementary ISDN services

Telephone Services:

Teleservices include Standard mobile telephone Mobile-originated Base-originated traffic. emergency calling Fax Videotext Tele text, SMS MMS.

Bearer services: The data services include the communication between computers and packet switched traffic. These services are limited to the first three layers of the OSI reference model. Data may be transmitted using either a Transparent Mode or Non-Transparent Mode. Transparent Mode:-Where GSM provides standard channel coding for user data Non-Transparent Mode: - Where GSM offers special coding efficiencies based on the particular data interface.

Supplementary ISDN services:

This service are digital in nature and include

Call diversion

Caller line ID

Closed user group

Call barring

Call waiting

Call hold

Connected line ID

Multiparty (Teleconferencing)

Call charge advice

This service also include the Short Messaging Service (SMS) which allow GSM subscriber and BS to transmit alphanumeric pages of limited length (160 -7 ASCII characters) while simultaneously carrying normal voice traffic.