You can buy very simple three terminal regulators. LM340-5, 7805, etc. Those are available at radio shack but they require a 2v overhead. You can buy low drop out versions from places such as digikey or mouser which only need a 1v overhead. then you can buy fancy switching regulators that will take a wide range of input + and - the output. Very easy to rig up a power supply with some of these.
Our current phones will charge from USB so I'm somewhat standardized there, could pick up any old computer system board or power supply and get a charge from it.