My query is below:
Each month my telecom provider gives me an excel list of all subscribers in the following format:
GSM number, account num, caller
As @joseph4tw says, you could do this with a pivot table similar to below (Excel 2010)...
To show all item labels, choose: Field Settings -> Layout & Print -> Repeat Item Labels
To create the sheet tabs just select Pivot Table Options -> Show Report Filter Pages (as below)
Update Having created the sheet tabs, you can use group editing to format as required...