SMS PDU-Mode
The Data-Coding-Scheme octet

Coding Group Bits 7..4	Use of bits 3..0
00xx	General Data Coding indication Bits 5..0 indicate the following: Bit 5 0 Text is uncompressed 1 Text is compressed Bit 4 0 Bits 1..0 have no meaning 1 Bits 1..0 indicates message class Bit 3 Bit 2 Alphabet being used 0 0 Default alphabet 0 1 8 bit data 1 0 UCS2 (16bit) 1 1 Reserved Bit 1 Bit 0 Message class Description 0 0 Class 0 Immediate display (alert) 0 1 Class 1 ME specific 1 0 Class 2 SIM specific 1 1 Class 3 TE specific NOTE: The special case of bits 7..0 being 0000 0000 indicates the Default Alphabet as in Phase 2
0100..1011	Reserved coding groups
1100	Message Waiting Indication Group: Discard Message Bits 3..0 are coded exactly the same as Group 1101, however with bits 7..4 set to 1100 the mobile may discard the contents of the message, and only present the indication to the user.
1101	Message Waiting Indication Group: Store Message This Group allows an indication to be provided to the user about status of types of message waiting on systems connected to the GSM PLMN. The mobile may present this indication as an icon on the screen, or other MMI indication. The mobile may take note of the Origination Address for message in this group and group 1100. For each indication supported, the mobile may provide storage for the Origination Address which is to control the mobile indication. Text included in the user data is coded in the Default Alphabet. Ehere a message is received with bits 7..4 set to 1101, the mobile shall store the text of the SMS message in addition to setting the indication. Bit 3 Description 0 Set Indication Inactive 1 Set Indication Active Bit 2 is reserved, and set to 0 Bit 1 Bit 0 Indication Type 0 0 Voicemail Message Waiting 0 1 Fax Message Waiting 1 0 Electronic Mail Message Waiting 1 1 Other Message Waiting* * Mobile manufacturers may implement the "Other Message Waiting" indication as an additional indication without specifying the meaning. The meaning of this indication is intended to be standardized in the future, so Operators should not make use of this indication until the standard for this indication is finalized.
1110	Message Waiting Indication Group: Store Message The coding of bits 3..0 and functionality of this feature are the same as for the Message Waiting Indication Group above, (bits 7..4 set to 1101) with the exception that the text included in the user data is coded in the uncompressed UCS2 alphabet.
1111	Data coding/message class Bit 3 is reserved, set to 0. Bit 2 Message coding 0 Default alphabet 1 8-bit data Bit 1 Bit 0 Message Class Description 0 0 Class 0 Immediate display (alert) 0 1 Class 1 ME specific 1 0 Class 2 SIM specific 1 1 Class 3 TE specific