SIMPLcase is a Kickstarter project that aims to make traveling with and iPhone and multi-SIM cards much, much, easier. According to the SIMPLcase page:
SIMPLcase allows the iPhone SIM tray eject tool, as well as up to three SIM cards to be discreetly and securely carried inside the case. With the SIMPLcase, you'll always have the right tool (we provide one with every case) and a secure place to store your SIM cards.
You can also use any standard card -- credit, debit, license, membership, hotel key, etc. -- as a convenient stand to better enjoy video or video calls on your iPhone while traveling. The outside is polycarbonate thermoplastic resin and the inside soft silicone rubber.
The SIMPLcase is currently being made for the iPhone 5, but they've prototyped one for the iPhone 4S/iPhone 4 as well, and are gauging interest for it via the Kickstarter page.
As someone who travels routinely, and switches SIM-cards fairly regularly, SIMPLcase looks to be a fantastic idea. They're roughly halfway towards their Kickstart goal, however, so if SIMPLcase appeals to you, and you want to see it made a reality, head on over and back it now.