Here are the items you will need.

1. Cheap throwaway mobile phone

2. Basic small solar panel (available at electronics stores)

3. Standard blocking diode (also get at the electronics store)

Attach the solar panel to the back of the phone with hot glue or epoxy. You can then burn a couple holes in the case with a soldering iron to run the wires through.

Next, burn some grooves into the plastic phone molding so that we can store the wires without them stopping the phone from closing.

Now the fun part!

Solder the positive output of the solar panel to the diode, make sure you wire it to the back end of the diode, (you can tell which side is which by looking at the diode itself). Diode's have a single white line on the end which designates the front, so just wire the solar panel to the side without the white line!

Next, wire the other side of the diode to the phone's positive battery prong (this should be marked on the phone itself). When that is done take the negative end of the solar panel and wire it to the negative battery prong on the phone.

Now pop in the battery and close up the phone! Your cheap emergency phone is now ready for action!