Use of Available in Touch in Visualforce
if checked in the Available in Touch, Visualforce tabs associated with the Visualforce page to be used in Salesforce Touch.
This checkbox is available in API version of 27.0 and later.
Standard object tabs that are overridden with a Visualforce page aren’t supported in Salesforce Touch, even if you select Available in Touch for the page. The default Salesforce Touch page for the object is displayed instead of the Visualforce page.