If you're on Textline's Standard plan or above, you can add custom fields to the contacts in your Address Book.
To add custom fields, click on Address Book at the top, then the Settings tab.
Enter the title of your custom field in the Custom Field Name box, select the field type you'd like, and click Create.
Once your custom fields are created, you can update the fields in your contacts individually or include the fields' information as you perform a mass import of contacts. For the latter, add the field names to the provided Address Book CSV template as headers of additional columns.
To edit an existing Custom Field, head back to the Settings tab in your Address Book, find the field you'd like to adjust, make your changes, and click the Update button.
To delete an existing Custom Field, click the Remove button next to the field you want to remove. Please note that deleting a field will remove it from all Address Book contacts and all data related to that field will be lost.
Note: If you don't think you need an entirely new field for each contact, but would like to label specific contacts differently from one another, Textline offers another feature that allows you to tag contacts.