Papier mache, crazy, huh?
I made some masks lately using papier mache, so when I was wondering around Instructables looking for a way to put my iPhone 3G in my car with style, I just thought I'd give it a try.
What I will do is basically a mold of the plastic tray the iPhone came in and then ellaborate a bit more to make it more like a case that can be placed in your car.
Of course, you can use this Instructable for any kind of iPod, MP3 player or cellphone, as long as you have somewhere to take a mold of the gadget.

What you will need:
iPhone (3G or original) plastic tray: from the packing the iPhone came in.
Paper: preferably from spam, catalogs or magazines, thick paper is best for a solid case.
White glue or any other glue: non-toxic, washable and is good for paper and using with your hands. I am using glue instead of the traditional papier mache paste because it is easier.
Vaseline: to apply the tray to make the mold.

Step 1: Apply Vaseline to the Plastic Tray

Apply a generous amount of Vaseline to the tray and distribute it evenly.
But do not apply too much, just make sure the Vaseline is everywhere.

Step 2: Cut the Paper

Using your hands, cut the paper.
This is better than using scissors, because when you tear the paper the edges are rough and it helps the integrity of the piece.
You don't have to cut specific sizes, but maybe from 1 to 2 cm. in triangular and rectangular shapes.

Step 3: Make Two Paper Trays

This is the fun part.
With your fingers, apply the white glue to a piece of paper and place it on the tray.
Carefuly, gently, put the piece of paper on the tray and make sure it follows the curves of the tray.
Apply gentle pressure to make sure there is no air trapped beneath the paper, but not so much that the Vaseline is squished from that area.

Start by making one layer. Pay attention to the unions of paper, so that there are no spots without paper.
Finished? let it dry. It might take a few hours, depending on your weather. It is very important that the first layer dries properly, so that it will help you keep the structure while applying the next layer.

When dry, carefuly pull the edges of the mold, so that the paper mold starts to peel.

MAKE ANOTHER ONE
You will use the second tray to complete the case.

Once you've finished with the second tray, you can clean and put away that plastic tray safely in it's box again.

Step 4: Reinforce Your Paper Trays

You'll notice that the paper trays are fragile, you'll need to apply more layers to make it more rugged.

Now, turn them upside down and clean them, removing the residual Vaseline and apply the next layer on the "outside".
The "inside" is where the iPhone is going to be.
It is "safer" in a way, to apply the next layers on the outside because if you achieved a good adjustment to the iPhone, you don't want to jeopardize that fit with the next layers.

So, apply a layer of paper with glue and let it dry again.
Keep adding layers until you are satisfied with the rigidness of the trays.

For added iPhone comfort, you could put some felt of something like it on the inside.

Step 5: Cutting a Tray to Complete the Case

You have several choices here. It depends on the type of case you want to have.
I wanted a case that would allow for easy access to the iPhone and would allow me to put it in Landscape mode if needed.

Experiment! if you ruin your mold, no matter! just make a new one and try again.

Anyway, mine has the bottom (allowing access to the dock connector and home button) and the right side, because the left side of the iPhone has the volume buttons and it allows me to put it on it's side for a Landscape mode/view.
So, I glued both trays, after cutting one of them for the access I needed.
Sorry I don't have pictures of this process.

You will probably want to cut the bottom to fit a power cord.
Even if you don't want to have access to the dock connector, you should probably open the bottom because that's where the microphone of the phone is (for free hand operation).

Step 6: Finish the Case

Paint it.
Use felt for the inside.
Use some textile on the surface.

Me, I am a guy of simple taste, so a matte black finish is just perfect for me.

Step 7: Put It in Your Car

Velcro is your friend!
Find a good spot in your car where you wouldn't mind gluing a piece of velcro on it and go for it.

Or, maybe you got inspired and attached something to the back of the case, like a wire, so that you can hang it from a vent.

Or maybe you modded the case so that it would fit a spot in your dashboard or somwhere else in your car.

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Enjoy your iPhone in your car and drive safely!!