fo help on a way to billing customers

[Gu Honghai]

We are a small ISP  , using such a way to billing customers :
A customer can buy a number of time ( i.e. 30 hours )  , then  he/she  can
connect INTERNET by our access server (use radius ) for 30 hours. When there
is 5 hours remained , send him/her a mail to inform his usage . when no time
left and he did not rebuy (30 hours) , delete(disable)  his account.


Does freeside support such a way to bill customers , and if it can , how to
setup freeside .( I have succeeded in installing  freeside)