The HLR/MTXH stores subscriber data for its subscribers. These data consist of subscriber categories and supplementary services information including «Prepaid Call Units». For a roamer this information is sent to the MTXV, using the Category/ Supplementary Services Updating Message (CSU).

The category/ supplementary services information can be updated in HLR/MTXH regardless of whether the mobile station is roaming or not. The Category/ Supplementary Services Updating Message, CSU, is used to update MTXV when changes are made in HLR/MTXH. MTXV answers by using Category/ Supplementary Services Accepted Message, CSA.