I've made a cheap and easy to build time lapse camera, using an old mobile phone, some java software, general firmware hackery and an old phone carrycase.
Most of the other timelapse camera mods I've seen on here and Make are based on wiring up a timer to switch the camera on, take a picture, then turn it off.
Thats good, but I cant solder for toffee, so I looked to a software solution...

Step 1: What You Will Need

Hardware:

Old Java (MIDP 2.0) compatible phone
Some sort of datacable for the phone
Phone carrycase

Software:

J2ME Development kit
FAR manager (optional - depends on state of phone)

Step 2: Write the Software

This is the hard part, believe it or not, there isnt any java based software that does this for phones. There are a couple of python based ones that will work on a Nokia phone, but not my nokia phone :/

I've attached the java files here, I'm NOT attaching the compiled versions though. If you're clever enough to compile/package these then you're clever enough to fix things if they dont work :p

Basically, it presents a menu where you can set the name of the image-set and the timelapse duration. It then spawns a timer that takes photo's and saves them on the memory card.

These are written with the SonyEricson W800 in mind. They should work with any midp2.0 compatible phone though

Step 3: (Optional) Hack Phone Firmware to Be Less Annoying

All apps that access the phone camera and memory must have permission to do so, otherwise they ask for it. Everytime.

Yes, that gets annoying so..

To fix this you have to "sign" the application, which costs money. Not interested! A cunning workaround is to hack the phones firmware to not prompt. Thats done with the FAR manager software and associated plugins

For the W800, the patches are here. They can ruin your phone if you dont pay attention. I'm not supplying instructions here, I dont want hundreds of "Lol I bricked my phone fix it plzzzz kthxbye" comments

My phone now no longer asks me for permission to run the software

Step 4: Use It!

Start the software up, on my phone its in the file manager, then "Games" (because of the rubbish transfer software)
Set the duration (I've chosen 60 seconds here)
Set the name (new, because I'm too lazy to type them)

Hit the "more->go" button and put the camera in the case. Wear it!

Step 5: A Test!

heres the first test, a standard time lapse clock gif :)

I did wear this on my bag whilst wandering to the shop, sure enough I'd left the lens cap shut. I'm planning some sort of strap to attach it to my bag strap and point forward. The pictures are about 30kb each and the camera has a 512mb memory card, so thats about 17000 pictures before it fills up. At 15 second durations thats about 70 hours worth of clips.

So I might just leave this on all day and see what happens :)