Personally I will buy one prepaid SIM when I am traveling abroad. This is cheaper than that using international roaming. Instead of remove the SIM tray manually, you can use this iPhone 4 Dual SIM Adapter Case for US$28.99.
Put the SIM cards on the tool and it can connect with the iPhone 4 like pictured above. Due to the limitation of iPhone 4 software, you can have both SIM cards active at the same time. However, you can easily switch to any SIM card in the Application Menu. One more photo after the break.
【Via Winandmac】
