We have seen some car phone chargers cause an error code to come up, I believe it was a U0002 code, which says there is voltage on the can-bus. Best bet is to remove the charger when it isn't being used, and especially before shutting off the key. Since the power port is disconnected when the key is off, no real reason to leave the charger plugged in.
I believe it was the Nokia chargers that caused the problem in the past, and only certain ones. The CEL could be reset with a code reader scanner (I used my ScangaugeII )