Reporting on a custom field


Can someone tell me how I can run a report on a custom field?

When you list contact and click on the edit search criteria button you will have a custom fields tab you can click on to define searches by custom fields. The options for each will depend on the type of field each is:

I can’t see how to do this for a Task. I can add the fields (specifically, for telesales result) but it is not available on the Call Log Report (which is the only place I can find Calls).