Dial some number like 112, make a call and immediately hang up using the red button. It won’t redirect to Home since the iPhone isn’t activated, however an option to make an emergency call will be offered.
However, activation of an iPhone requires a valid SIM card and you can’t activate iPhone without sim card inside the phone, like it could be done in iPads and iPod Touches.
IPhones are great gadgets to begin with, and there are no doubt about the security, integrity and the features offered on these devices.