The *output* voltage of the charger would be. Most now are designed to charge off USB, which is 5VDC. Most adapters now are regulated PWM-switching types, which will take input voltages anywhere from 100-240VAC.
A bigger problem with the Nokia would probably be whether the two use the same physical connector...
AFAIK, Nokia is one of the few that HASN'T moved wholesale to USB charging jacks and still use their own designs, and from the Nokias I've had in the past, they seem to like to change the connector every couple of model years.
Either way, if the connector fits, you should be fine.