So you want to use two SIM cards with your phone? The Krimston TWO can help. It is a dual SIM iPhone case that not only lets you use two SIM cards simultaneously, it also keeps your phone powered up for longer. You will be able to have your contacts synced for both SIM cards.
The Krimston TWO case does not look too bulky and lets you maintain two lines for any reason. The product is currently getting funded on Kickstarter.