Can you still see old messages on an old SIM card for an iPhone 4? Mine died a few months ago, AT&T techs took out the SIM card when they gave me my new phone, but now my parents are trying to "fix" my old phone to be nosy! Yikes!
Assuming you didn't wipe your phone before removing the SIM card, your messages (and everything else) will still be on the phone. If your phone is still registered in "Find my iPhone" and has network connectivity (either through a new SIM card or through WiFi), you can wipe it from your iCloud account. See iCloud: Find My iPhone overview and iCloud: Erase your device for details about the procedure.