Because the Nokia 6100 is a GSM phone, you can store phone contacts either on its SIM card or in the phone's memory. In order to transfer the contacts to another phone you will need move all your contacts onto the SIM card.
Click the "Menu" button on your Nokia 6100 phone and from the next screen select "Contacts."
Scroll down the Contacts options until you see "Copy Contacts." Click on this option and select "From Phone to Sim." The message "Copy Contacts?" will appear, and you should click "Yes." The contacts will now copy to your SIM card.
Switch off your Nokia 6100 and remove the SIM Card by sliding the back off the phone, lifting the battery and sliding it out of its housing. Open your new phone and place the SIM card into it.
Power up the new phone and go to your Contacts or Address Book folder. The name may vary depending on what make and model of phone you are switching to. You will see the contacts is now populated with your SIM vontacts. You can then copy these into your new phone's memory by using a similar procedure in reverse. Again, the precise wording may change depending on the new phone's make and model.
Ensure that your new phone is compatible with your old Sim. It will need to be from the same network provider or the new handset will need to be unlocked. You can leave your contacts on the Sim, they don't have to be copied onto the phone.
Always keep a backup record of your contacts just in case you lose your phone.