11-25-2013 05:09 AM
11-25-2013 09:05 PM
Welcome to http://supportforums.blackberry.com/
It is recommended that you use a SIM card that is compatible with the 9900
Total SIM card not only that you will keep more contacts.
If you want to return to your 8520 decision is yours, but the improvements fijate have a 9900 and its capabilities and specifications.