When it comes to a cell phone battery charger I always buy a trickle charger. This way it will stop charging when it is completed and will not overcharge my phone. I think this also helps the cell phone battery last longer.
I used to be more careless about my cell phone charger, but I had one that overheated one time, so now I always use a trickle charger.
I also had someone tell me once that it wasn't safe to talk on your phone while it was charging. I don't know if there is any truth to this or not as I have never had any problems doing this.