This supplementary service provides the MS with the information to produce an estimate of the cost of the service used. Charges are indicated for the call(s) in progress when mobile originated or for the roaming leg only when mobile terminated. Any charges for non-call related transactions, and for certain supplementary services, such as Call Forwarding are not indicated.
The MS will receive at the beginning of each call (and as necessary during the call) a message, the Charge Advice Information. This message contains the elements which together define the rate at which the call is to be charged, time dependence, data dependence and for unit increments - see TS 22.024
The MS shall still indicate appropriate charges even when roaming, based on Home PLMN units.
Where applicable, the volume charge for Packet data service, in addition to the normal time dependent and incremental charges, shall be indicated.
To indicate the charge per call the Mobile station shall display the units consumed so far during the present call(s) and maintain this value until the MS is switched off or a new call set-up is attempted.
Where required to indicate the total accumulated charge, the MS shall be able to display, and the SIM/USIM shall store in the ACM, the running cumulative unit charge. This value must be stored securely, and all reasonable steps shall be taken to ensure that the written value cannot be interrupted, reset or corrupted (except resetting under control of the unblocking key).
The applicability of this supplementary service is defined in TS 22.004