Ok so just to explain myself i'll tell you the full story, I had an iphone 6 plus, then I bought a brand new iphone 7 plus, I removed the sim card from the iphone 6 and inserted to the brand new phone, then restored everything from itunes via backup to get all my files/photos/apps from my iphone 6 to iphone 7, so everything was setup perfectly. The iphone 6 is now without a sim, but is still opened and connected to a Wi-Fi, and my sim card is now is used by iphone 7 plus, the new phone. Now to my surprise, when my phone rang, both of the phones started ringing, simultaneously. I was shocked, thinking it was a feature of the new iphone, if both were connected to the same iclouds & conncted to a wi-fi. To test this further, I asked my wife to call me again, and I've spoken with her via both phones, both worked fine during the voice call, btw, it wasn't a whatsapp call, or any internet application call, it was a sim_card company normal voice call, and it worked on both phones, I was happy with this feature and liked it, wanting to taste this further, I closed the wi-fi connection from the iphone 6, and it stopped working for the sim card line, re-opened wi-fi, and the phone rang whenever my iphone 7 rings, the iphone 6 rings too, to make sure the sim card is working, I even tried the normal TEXT messages, if i receive one on the iphone 7, the same exact TEXT message will be shown on the iphone 6 too. Days later, I tried it again, and it stopped working completely, sorry for the long message here folks, but really my question is, was this a glitch? is it a feature? if it's a feature how to enable it again, my iphone 6 stopped doing what it was doing on day 1, being synced with the sim card of iphone 7.