your iPhone cannot be accessed without an active SIM card. If you turn on without a SIM it would keep asking you to insert an active SIM card. If your iPhone 3GS is network locked you must insert a SIM card from same network. If it is unlocked, you can insert any active GSM SIM card. To unlock a network locked iPhone, you can visit mobileunlocksolutions.com and get the remote unlocking service at affordable cost. Good luck.