A system comprising: a vehicle head unit, the head unit implementing at least one type of generic application display screen; a server computer, the server computer arranged for communications over a mobile network to a mobile phone; a handset application proxy software application executable in a mobile phone; and a head unit proxy software application executable on the head unit; wherein the server computer is further arranged to deliver phone application information associated with a specific user application program executable on a mobile phone, and the server delivers the phone application information to the mobile phone via the mobile network; wherein the phone application information enables extending a user interface of the specific user application program to utilize the generic application display screen of the vehicle head unit; and wherein the HAP and the HUP are arranged to communicate messages or events between them, and to utilize aspects of the phone application information to enable the specific user application program on the mobile phone to interact with the generic application display screen of the vehicle head unit, wherein the handset application proxy software application and the head unit proxy software application are each implemented in a scripting language, and wherein: the HAP includes a message handling component, and at least one protocol stack coupled to the message handling component, for communications with the head unit; the message handling component includes at least one scripting language component associated with a specific user application program; and the scripting language component includes a corresponding template message translator component, the message translator component configured for translating request and response messages generated by the corresponding user application program into a format compatible with a template-based generic application display screen(s) of a vehicle head unit. a vehicle head unit, the head unit implementing at least one type of generic application display screen; a server computer, the server computer arranged for communications over a mobile network to a mobile phone; a handset application proxy software application executable in a mobile phone; and a head unit proxy software application executable on the head unit; wherein the server computer is further arranged to deliver phone application information associated with a specific user application program executable on a mobile phone, and the server delivers the phone application information to the mobile phone via the mobile network; wherein the phone application information enables extending a user interface of the specific user application program to utilize the generic application display screen of the vehicle head unit; and wherein the HAP and the HUP are arranged to communicate messages or events between them, and to utilize aspects of the phone application information to enable the specific user application program on the mobile phone to interact with the generic application display screen of the vehicle head unit, wherein the handset application proxy software application and the head unit proxy software application are each implemented in a scripting language, and the HAP includes a message handling component, and at least one protocol stack coupled to the message handling component, for communications with the head unit; the message handling component includes at least one scripting language component associated with a specific user application program; and the scripting language component includes a corresponding template message translator component, the message translator component configured for translating request and response messages generated by the corresponding user application program into a format compatible with a template-based generic application display screen(s) of a vehicle head unit.