Here's what I've found via experimentation.
Pin 9 is RxD (Nokia receive input) and pin A is TxD (Nokia transmit output). These are the third and second pins from the right towards the battery, respectively.
I used the metal shield as a ground. The outputs are evidently 3.3v - I used a USB-mobile phone cable as described in http://www.nslu2-linux.org/wiki/HowTo/AddASerialPort
to connect to the device.
I enabled the R&D mode and set the serial console flag and connected via 8N1,115200.
I don't know of a suitable connector - I used a couple of stiff wires held in place with electrical tape.