Yes the @PrintByXerox App will work on a Xerox 7220i without the PS kit. You can install the App from the Xerox App Gallery here: https://appgallery.external.xerox.com/xerox_app_gallery/solutions_market_place
Please let us know if you have any trouble using the App on that device.
Does the print@printbyxerox app work on a Xerox 7220i that does not have the PS kit on it? The software version is 073.030.075.34540.