You can. We know that you may need to sort contacts based on some information that the list currently does not display. Changing the grids makes it harder for the app to respond properly in other tables such as Sonar, so the contact list is the only grid with this feature.
If you click on the "Contacts" tab in the Contact Relationship Manager (CRM) or view any list of contacts, you can click "Edit Columns" in the upper left. Once there, click the blue "New Column" tab, which will allow you to create a new custom field. Once the settings are in place and the column created, you can even sort your list using the new field.
Absolutely, there are no added costs.