The e808 attaches to the computer via a USB cable. A WDM(Windows Driver Model) is installed, called "NEC 808 USB Controller". The "NEC e808 PC file transfer" software communicates with the WDM via a virtual COM port, which in turn communicates with the phone. The virtual COM port may be accessed similar to the physical com port(namely through API calls). This opens up the possibility of writing one's own software to communicate with the phone.
NEC e808 PC interface - Programming details for uploading files to the e808 phone(PDF).