yes, miilamps 1 amp is 1000 ma.
What this means is if the phone is off and hooked to a oem .7 (700ma) charger, it will go from 0 battery to full 1500 in a bit over two hours. About 3 hours on a computer usb which is normally 500 ma.
But if the phone is one it can be itself pulling 50 ( a rough guess at standby under average Rf) to 600 ma (I bet wifi, GPS full time, 4g, full bright screen and blutooth might pull even more).
I've have had phones that will discharge on 500 ma usb connection while using wifi and 3g.
I use the 700ma sammy charger on my home desk, a 1 amp charger at my office, but have a generic cheap 300 ma charger in my bedroom since that is fine for overnight.
But for a car charger go with .9 to one amp if you are using your epic for nav. that way if you pop into your car at 25% and go for a half hour ride you will probably come out at 50%
the thing with ebay and motorola chargers is that there are a lot of very well concealed counterfiets, and you wouldst use a reputable dealer.
the good news is the investment in micro usb chargers is fairly efficient since chances are your next phone or any of your friends that need a charge will be micro usb as it is now widely a standard.