Creating Mulitile Billing documents based on Sales order

Hi All

My requirement is to create a billing documents based on sales order. Item category is SERVICE.

For example : In Sales Order the quantity is 100.

1 st billing doument user can create of 10.Then after 1 month 2nd billing document of 9 and so on.

when i create billing document related with sales order . the billing document is created with 100 quantity.

i know it is possible with delivery but my requirement is billing document should be created related to service.

Appreciate your time.

Thanks and Regards

Mahesh