A mobile subscriber can activate or deactivate subscriber controlled supplementary services using his mobile station.

Data about activated supplementary services is stored in HLR/MTXH.

Activation or deactivation of supplementary services may be done when mobile station is roaming.

Signalling using the following messages is applied:

• PSR, Pre-Supplementary Services Registration/ Cancellation message
• PSA, Pre-Supplementary Services Registration/ Cancellation Acknowledgement message
• SRM, Supplementary Services Registration/ Cancellation Message
• SRA, Supplementary Services Registration/ Cancellation Acknowledgement message

When MTXV receives supplementary services registration/ cancellation information from a roaming mobile station, the information is sent transparently to HLR/MTXH, i.e. the information is coded into the PSR and the SRM messages.

The PSA/ SRM messages are linked together as one transaction by means of the Transaction Reference field and the Transaction Number in the PSA and the SRM, the same Transaction Reference and Transaction Number is used in both the PSA and the SRM.

• In the case where no Category/ Supplementary Services updating of MTXV is necessary, send PSA in response to PSR and
• in response to SRM send SRA including information about which audible information is to be sent by MTXV to the mobile station, (fig. 3.5a)

• In the case where Category/ Supplementary Services updating of MTXV is necessary, initiate the category/ supplementary services procedure as described in paragraph 3.4, before sending the SRA (fig. 3.5b).

When sending the PSA a timer T3 is started.

If the SRM is not received before T3 expires, the PSR already received shall be discarded and the procedure in the MTXH terminates.