O problem of the Bumper cases, for the GSM version of the iPhone 4, was that certain 3rd party chargers could not be used as long as the case was mounted on the terminal. Apple chargers were the only ones that could be inserted properly through the opening at the base of the case because it was specially designed to work only with this kind of accessories. If you had a charger made by Griffin, Zagg or any other third-party manufacturer, then it is very possible that it cannot be inserted into the terminal if you have an old Bumper case. The new Bumper cases specially made for the iPhone 4 CDMA terminals have a much more even opening at the bottom, allowing the insertion of any model of charger.
In conclusion, if you encountered the problem explained above when you try to use a 3rd party accessory, then maybe you should think about changing the Bumper case with a new one.
