credit cards

The fees and interest you pay for credit card cannot be considered as an input for your  output service. You use credit card for your convenience / expediency. Service tax on phone / internet can be considered but the membership fees, late payment and revolving interest on a credit card cannot be considered. Say you lose the card and replacement costs, where will it have a nexus to your service. You will have to connect each individual charge.

If a professional has to bill his out of pocket expenses like say cost of air ticket to a company and he also has to bear service tax on this reimbursement, if he has paid through credit card and has been levied a transaction fee for purchase of the ticket to his client incuding the transaction cost on credit card with service tax, then the transaction cost has a nexus to the output service and can be termed as an input.

You will have to make an undisputable connection.