How to enter email/fax on the purchase requisition to flow to purchase order ?

  We have a case were purchase orders are automatically created using contract agreement once the purchase requisition is approved.

Problem

Need to change the communication information like email/fax number automatically created purchase orders using contract agreement

Desired solution

User should lbe able to enter the email/fax for the supplier when the requisiton is created against the contract agreement. Email\fax information entered on requisition should flow to purchase order automatically created.

Thanks,