A 'Model A' Raspberry Pi 
a tft screen [http://www.adafruit.com/products/1601] 
and a Arduino gsm shield 
It was a fun experiment to do, and in the end, it did gave me a "phone" i can use.
Unfortunately, it became so big and heavy, that it is
more something to put on your desk as a clock and have it send text
messages on all kinds of events. Or receive text messages and perform
actions upon receiving. Also, battery life is not good. The 8 rechargeable
penlight cells will only last for 3 hours.
I tried to use off-the-shelf components as much as possible, so no hard to get li-ion battery packs, but plain and simple penlights. and mini USB to provide power, so any usb charger will work.
I took the pi, removed the rca and earphone plugs
then drilled a hole in the tft PCB, so i could solder the pins of
the pi onto the tft pcb.
The Arduino gsm shield is
almost as big as the pi , so to stack one on top of the
other seemed the most logical way of putting it together.
To get some kind of shielding between the GSM antenna, and the pi,
i decided to make the case out of "etch it yourself PCB".
The casing is made in compartments, not unlike the Matryoshka dolls
[http://en.wikipedia.org/wiki/Matryoshka_doll].
The first cup
was to hold the electronics
to charge the batteries on the inside, and to hold the GSM shield on the
other side. There are two "power suplies" (dc/dc convertors and
voltage regulators). And you realy need to power them both to
charge the battteries and power the pi and GSM shield.
To give the antenna free "line of sight" to a GSM tower, a second
cup was made, with a plastic bottom.
Then another cup was made
to hold the first cup and mount
the batteries on.
And then a last cup was made to hold the display and pi.
The pi was placed in the topleft corner of this cup, so the USB
and HDMI connectors are still usable.
And to finish it off, i used teak veneer, to make it look
more decorative.
I hope it will inspire someone to make a better, smaller version, with better battery life.
The old site is here