On a core contribution page, if you add an address profile at the top of the page, a checkbox appears allowing the user to indicate that their billing address is the same:
On a Webform-CiviCRM form, my understanding is that the payment page is always a separate page and this box is not automatic. Is there any way to include a checkbox like this?
This feature has not been implemented in Webform-CiviCRM. If you do see that box in a webform, it's a mistake (and the fix is to remove profiles from the contribution page you are using for the webform).
Implementation of this feature would require writing some javascript to fill those fields from available data, and some php code to store the data across potentially multiple pages. The best place to put it might be in wf_crm_webform_preprocess::addResources.
Note that if the user is logged-in then the billing fields will already be pre-filled.
