We need a way to be able to apply a discount per item if need be.

For example, say we are a phone company and sell the following as add-ons:

2 phone lines
1 fax line
2 additional phone numbers

We would like to apply a 5 dollar monthly discount on the fax line and a 10 dollar discount on each phone line and a 10% discount on the phone numbers.

Perhaps this could be achieved by allowing multiple coupons to be applied per subscription as per another suggestion.