The 3310 couldn't be connected with a standard data cable, it didn't support that feature (it was too basic).
If you take the sim out of your 3310 and put it in the 6120c you should be given the option to copy the contacts into the new phones memory. This may not happen if the 6120c won't accept your old sim.
The old sim may also be compatible for use but you may experience difficulties with some services.