RS232 is not really the right term here. None of these cables produce the inverted 12V signals for proper R232. They do 5V TTL levels (or 3.3V with 5V compartibility) just as an FTDI chip would do. This works great for direct connection with the UART of an Atmel Microcontroller.

Nokia CA-42 / DKU-5

This cable has 7 wires, but only 4 are connected. The Photo below shows where I did cut open the soft plastics (between sticker and tail) to reach the place of the PCB, where the unused pins are. I’ve connected some of the unused wires to give me a cable with handshake signals.

I keep forgetting the pin out all the time. Here is the color codes stored for eternity:

Black:    (7) GND

Blue:      (3) RxD to USB Host

White:    (2) TxD from USB Host

Orange: (10) +5V

Green:    (9) [DTR/RTS] from USB Host

Red:       (8) DCD to USB Host

Brown:    (5) ???

The question marks are some Handshake signals. The numbers in parenthesis are the pin numbers on one of the PCBs I have disassembled.
Retail price May 2013: ca. 3.33 EUR

MQ Power USB Datenkabel für Siemens DCA-510 S55 / SL55

This is a newer cable for a Siemens S55 Phone. The cable has only for wires, although the PCB has a 5th pin for a handshake signal.

Yellow: Ground

Red:     +5V

Green: RXD

Blue:    TXD

— :      DTR

This cable sends continuous garbage to the USB-Host, if the green wire is left floating. You can prevent this, by dropping e.g. a 430K Ohm SMD resistor (not shown above) between the soldering pads of RxD and GND.

As of May 2013, this cable can be bought for as low as 1.49 EUR; google for the german title above.