Deducting phone bill amounts from expenses

Hi,
First of all thanks for making a great product! I have just started using zoho for our business and trying to figure out all its features.
We have a bunch of drivers that we need to pay at the end of the month through an expense acct called driver expense. But since we provide them cell phones we pay a fixed part of the phone bill and the remaining is deducted from the driver's payments. Then the full phone bill is paid to the service provider through an acct called phone expense. We want to raise a bill for each driver and then make a payment against it. But before making a payment we will deduct the phone bill and then pay the rest.
How can I achieve this with zoho?

Thanks
Avinash