e-invoices via OSN

 Is anyone using OSN for the delivery/receipt of electronic invoices without the receipt/delivery of electronic purchase orders? 

Our situations:

1.  a computer supplier often times has negotiated prices with us (not the same as their catalog) so our orders to them do not have catalog prices.

2. the vendor may not have an electronic catalog and thought is that price discrepancies may cause more issues than benefits by sending them orders via OSN.

3. non-purchase order types of purchases such as telephone bills.