By double clicking on the task in the call sheet the task details screen will show.

Here you have the ability to schedule the task, assign the Supplier and add in the instructions for the supplier.

When hitting save the callup will be sent.

Note: If you clear the planned date and click save it will send a cancellation message to the supplier. Once the planned date is removed you can delete this task if needed

2. an alternative would be to use the contract scheduler to drag and drop tasks into the Calendar:

first go to the Contract scheduler:

Then drag and drop the task in

now go into changed items to approve sending of the callups.