[the_overlord]

all these phones have smart charging circuits and smart batteries. you can charge your phones safely from any 5V mini USB source. The power supply is not an issue for the phone. As far as the current rating of the power supply is concerned the lower the output the longer it will take to charge. And if the phone is pulling more current then the power supply can put out it will continue to drain the battery even while plugged in. But, there is another thing to consider. That being said, some power supplies have sensing feedback from the phone and will not turn on unless it is plugged into the correct phone.
I have even been able to charge my phone with the power supply from by Motorola bluetooth headphones when it was in flight mode, but it took a while.