I have an old iphone 4s that has tons of issues with the battery. But also it lags a lot. I use whatsapp there with my mexican cell phone number. I have a mexican sim card in there that i use in mexico. I call and receive calls to and from the us with google hangouts number. I also use wechat as well. I will be using my new iphone SE. However, i want to backup my iphone 4s because i want to factory reset it to see if that could possibly fix the battery issue/lagging issue. Then store it with the backup from my itunes. First off if i do this, then everything in my iphone4s should look exactly like before i do the factory reset? Thus all my numbers, whatsapp and wechat will have the previous messages and contacts etc with nothing changes? On my new iphone, its an SE so i will have to buy a new sim card on it because the old sim card will not work. Now if i want to transfer whatsapp and wechat to this phone, can i do this? Do i just upload the backup from itunes into this phone? The thing is with whatsapp, you are suppose to confirm with them that you are the owner of the account right since whatsapp uses a phone number? For example, if i get a new sim card with my iphone SE in mexico, if i get a new phone number, could i transfer my whatspp number to the new number? Or if i use whatsapp on this new phone, i have to get a new account? I heard someone mentioned you can do this but you have to prove to be the owner of the whatsapp account on my other phone. So how do i even do this? Does that mean if i do this, then i have to transfer the same phone number on my iphone 4s to the iphone SE when getting a sim card for the SE?