0. Disclaimer
I hereby disclaim any responsibility for what happens to your N10. As far as I know, the information stated in this document is correct, but if you demolish your N10 by using this howto in any way, you're on your own. This hack has not been tested in WinCE and only little in Linux.
This modification will probably void the warranty on your N10.

1. Introduction
The N10 has a serial port. It might not be obvious at first, but one who looks around a bit in WinCE sees that the OS reports a COM1. Unfortunately the serial port isn't available as a handy external connector. In this howto, we'll try to remedy that situation.

2. Needed stuff
You'll need:

3. Putting it all together
The N10 serial port can be found at CN2, which is found on the position of the compact-flash-slot but on the other side of the PCB. It's possible you'll have to remove some black tape-like stuff to properly see it. The pinout is:

(Click for a larger image)

Ok, now we'll need to make some room for the connector. I figured the best place to put it would be under the jogdial and irda-module. For the connector to fit there, you'll have to cut off a bit of plastic from the thing the battery is sticked on:

(Click for a larger image)
You'll also need to remove a bit of the black plastic the sides of the N10 are made from and a tiny copper contact:

(Click for a larger image)
To hold it in place, solder the bottom pin of the header to the pad the copper thingie was on. That pin will be the ground. The pad already is a ground point, so you won't need to run a wire from cn2 to that one. Now the other pins will be connected with the thin wire, I used the following pinout:
1 (top)Nc
5 (bottom)Ground
In these two rather bad pictures you might be able to see how I did it:

Finally, use some superglue / 2-component-glue / other strong glue to make sure the header stays in place:

As soon as the glue has dried, you can put the N10 together again.

What to do with it?
Before I go and explain what's possible with the port, one word of warning: This port is 3.3V only! If you'll hook it directly to your PC or 5V TTL-thingie, your N10 might not survive it.

To get your serial port to connect to e.g. your PC, you'll need a thing called a 'level converter'. I used a hacked Siemens C35 data-cable for it.

ToDo: More examples & schematics