GPL versions of WURFL PHP API libraries are ready to be downloaded from here .
Version 1.1 is the one integrated in Zend Framework Zend_Htpp_UserAgent component.
Version 1.2.1 is the latest released under GPL license.
Later Edit: removed because A) AGPL version is available, but you'll need to download it for yourself and B) removed to make Luca Passani a favor :-).