cut my cable in half.
Hope you cut it near the phone end, so you get a longer cable.
I did tie both the the RX & TX lines.... open Hyper terminal and infact get text on the screen.. however it wasnt being duplicated (although I dont believe I had on echo default)
Also cut the RX-TX connection while in hyperterminal, and verify that you dont get any echo / text back.
Dont measure voltage, measure continiuty on the "phone end" of the cable, to map out the connector to wire color. Seems like you have done this though. So according to your map, wh (white? pin 7, TX) goes to the arduino RX. gr (green? pin 6, RX) goes to arduino TX.
But I would use 1k ohm resistors from the arduino TX and RX, just in case you switch wires and get an output to an output..
Also, is your arduno 5V or 3.3V? If 5V, you should use the 10k - 15k voltage divider as pr the schematics in your first link, on the arduino TX output, which goes to the green wire (RX) on the cable.
If you don't have an auto-reset, you would have to figure out when to press the reset button before / right after trying to upload a sketch. Depends on the bootloader. I find it usually works if I press "upload", then the reset button right after. A one-handed operation.
I have a DKU-5 btw.