"Volvo will offer an application for their smartphones that replaces the physical car key. This app will connect to the vehicle via a Bluetooth link. Benefits, according to the carmaker, are more flexibility and new options to share cars. The digital car key can be copied by the authorised user and transferred temporarily of permanently to other persons. In the case of a loss, it can be revoked remotely."
http://www.eetimes.com/document.asp?doc_id=1328996