Incoming call on 2nd iPhone without SIM Card Yesterday, i was going to setup my new iPhone 6.
So i did a backup of my iPhone 5, exchanged the SIM card and restored the iPhone 6. The restore did not went well, so i switched put the SIM card back to my iPhone 5.
I left both phones switched on.
Now, whenever i receive a call, both iPhones ring. And i can connect the call on either iphone. How is this possible?
iOS 8 has this new feature called Continuity. Which basically means you can make and receive phone calls on your iOS devices as long as your iPhone is on the same Wi-Fi network.


Source: Apple

Go to the phone with the active cellular SIM and you can disable this in settings app:


Phone
Calls on Other Devices
Allow Calls (turn them all off or disable some but not all other devices if you prefer)