I've got that Turbo Charge thing, which NightHiker has mentioned a while ago (thanks!), very cheap on eBay with a bunch of connectors for all of my 3 cell-phones. I believe, that the primary problem is actually the phone plug (I have exactly that weird USB powered Motorola phone, mentioned above, and two different Samsungs). It's not always easy to improvise a reliable connector, especially in the field.

Here is my solution. I have all of my chargers wires cut near the phone/PDA/MP3/Radio/GPS/PSP/Camera/etc connector and rejoined back with widely available 3.5mm audio connector male/female pair (kinda bulky, thinking of switching to 2.5mm as on the Turbo Charge thing). Most of these devices needs 5V of charging voltage, so, I'm carrying the single 110V/5V wall adapter, 12V/5V regulated car adapter (regulated means that you can get a stable 5V output from any 9-24V DC input, not possible with a single resistor solution, mentioned above), and the PowerBank thing (which is basically a compact 3600mAh rechargeable battery with regulated (1.5V-12V, 0.5V step) output and 12-24V charging circuit). - Everything with the matching 3.5mm audio plug. Plus, some weird USB/3.5mm charging wireloom cable pair compatible with everything on the picture (just some job specifics ). I'm also have a couple of Y audio splitters allowing to charge 2-3 gadgets simultaneously.

Only some of the connectors are shown on the image (others are in the car at the moment). The bare wires plug is also included (small coil on the bottom left). I'm usually charging the PowerBank first (with solar power in the field) and then, everything else: