So...mscion...
here it is simple.

You will want a headphone / microphone jack that plugs into your n900 headphone jack...
it splits to separate female headphone and microphone ends.
like this one ...for example....which are very cheap and plentiful..



buy 10 for for under $10
Or spend a few dollars and get a decent one...
I would suggest a couple ...always good to have spares.

You may want a pair of headphones or ear buds with a good long length of cord to them ...depending on where and how you wish the n900 to sit while playing..


You will want a couple 3.5 mm male to 1/4" female adapter for the mic in ...on the splitter ...so you can plug your guitar or oyster pick up into it. (depending on the types of instrument you enjoy playing..)
and possibly the headphone out to an amp if you desired..
Like this one...



yet again you can find stupidly cheap ones...
I would suggest paying the 3 to 5 dollars ...decent versions..decently plated..and grab a couple of them...have some spares.

Ebay will get you what you need quick and cheap...and as good a quality as the pennies you wish to spend.

All told if you end up paying more than $10 for 2 splitters and 2 adapters ...then you are aiming for decent ones...

Now...
you are good to go.

GTKgep installation is easy ...

https://talk.maemo.org/showpost.php?...9&postcount=50

download, install it and run it via terminal ...just typing gtkgep never started it for me...
I just type in the longer string of command and it does.
Annnnddd
Awaaaayyyy
You go.

You'll have fun with it ....promise.

Me...
It depends ..
I have some stereo pick ups for my harps ...and oyster pick ups too.
And either run the pick up through my tuner first ...
then out to one of my extra n900s that I have put velcro on the back of...
and a square of velcro on either the side or pillar of one of my harps..(depending on the harp...) so it is conveniently close and secure from getting knocked around.
And then out to an amp ..
or out to my earbuds..
or out to my laptop for more fun...or recording...or whatever...and then out from there yet again to earbuds or an amp...

In the end...though ...it enables a lot of good loud light portable fun on the go with the n900 in your hand...that you can enjoy with earbuds...without deafening others...
If that is the end goal..of course..