where can I buy a sim card for my nokia 3390?
If your Nokia 3390 is free from network restriction, You can choose a network and visit it's nearby retail store. They would guide you with the remaining process. If your Nokia 3390 has been restricted to any network, Visit the respective network provider and get the SIM card for it. If you wish to use any other network on your Nokia 3390, You need to unlock it in prior. You can unlock a Nokia 3390 safer and easier using unlock code. You can get the unlock code for a Nokia 3390 from http://www.simpleunlocking.com/nokia-3390/rs16wp9/ at affordable cost with easy unlocking guide. Good luck.
Go to the place where you bought your phone (that is if it is a cellular phone store) or any other places that sell cell phones.