Serial. Not tested
Rx is at Nokia pop-port pin 6
Tx is at Nokia pop-port pin 7
GND is at Nokia pop-port pin 8
check http://www.ftdichip.com for usb port converter drivers
Original DKU-5 cable is the older design with serial port emulation and there is a speed limit at 115200bps. The cable connectors are in Black color and the USB side is about 7cm in length, which is longer than DKU-2 or CA-53. The current version of Nokia PC Suite NO LONGER supports DKU-5.
Original CA-42 cable is the replacement of the DKU-5 for most newer compatible cell phones. It eliminates the software emulation but doing the Pop-port to USB conversion right at chip inside the cable. It behaves more like a true plug-n-play. Speed limitation is 230400bps. The cable connectors are in Blue color and the USB side is about 7cm in length, which is longer than DKU-2 or CA-53.
Both cables are not for charging - data connection only.