I bought this charger at a Radio Shack store. It has a right angle mini-usb plug, that plugs into the side of the blackberry, and goes down instead of sticking out like most other mini-usb chargers. But I'm not sure if the voltage is the same, and if it could burn my phone. I would think that if it's mini-usb the voltage should be the same, but how can I be sure?

You need to read the plug and see what the voltage output and current output are. Then compare that to the BB charger.

i use it...no problems

You are safe, charge away!

All USB charger (car or not) are 5V (+ or - some change) so they wouldn't fry your BB. I believe it needs to be at least 700mA (I think that's what I read on the back of the AC charger) or it won't be able to supply enough power. The more the better in this case.
Most GPS car chargers are rated at 1000mA, so they should be able to supply enough power.

You can charge with 500mA, just a much slower charge.

I see, thanks a lot guys!