I have a Cell Socket for the older Nokia 5100 series phones. I stopped using it because even though it supplies power to the phone, the phone thinks it's in CAR mode and it shuts off when the battery is fully charged by the socket. I have a Nokia 5190 phone.
I believe it is wired or programmed incorrectly - the actual car socket (I have one in my truck) has an ignition detect circuit and the phone will shut off a few seconds after the ignition is shut off, unless you hit a button on the phone.
So just be careful of these units - make sure you have a satisfaction guarantee and a good return policy wherever you buy it from in case they don't work as you expect.