Make a Note of Your Contacts
When I switched to a new SIM card, my contacts didn't transfer over. My text messages, which were saved to the phone and not the SIM card, did, so I could figure out most contact numbers from those. Don’t forget to write down any contacts you'll need abroad if you haven't saved them to your phone. Most things (like log-ins for email and Facebook) were saved to the phone, so it was a pretty seamless transition between SIM cards.