Hi Jaideep,
Interesting question but probably in wrong thread.
For the Cable subscriber, you will have to charge based on the plans + channel etc selected.
All these should post to your Customer Invoice and he should validate it.
Check SAP Convergent charging solution for this.
Another point will be the leasing related process for the set top box given by the company,
Check SAP Leasing Solution too 
Finally all these and normal AR related process will require a contract type accouting for the customer and this you can achieve with SAP FICA.
The best part is SAP FICA works well with both the above solution.
Hope this helps, if so please close this thread.
Regards
Rishab