Unlocked IPhone 5. Can be ported to one GSM provider but not another. Why?

My friend in South Africa got an AT&T model of Iphone5. It is now unlocked and has been ported to one of his providers. He doesn't like the data rates and wanted it on either "Cell C" or "8TA" (which is Telecom Mobile) Both are GSM providers I believe. So why can the phone be ported to one GSM provider, but not the other? Should the Iphone 5 be possible unlocked in a different fashion?

Added (1). he assures me, it should work on the other networks in SA.

IPhone 5 screen won't turn on?

My iphone froze while I was on the Internet so I locked the screen and now it won't turn back on. The power button stopped working about two months ago so I've been using assistive touch but the home button still works. The phone is charged and its on because I can hear Siri when I hold the button and when I tried calling my phone it vibrated and made sound like it should but the screen is still black. I've tried plugging it in but the screen stays black, I tried calling apple as well but apparently there's business hours so that's annoying. Is there anything I can do to make the screen show up?

Can i put ipod back up onto an iphone?

I have an old ipod 4 running IOS 6.1.6 I'm getting an iphone 5s that would be running the latest version of IOS 7. Would I be able to back up my ipod to itunes and then sync my phone as an old device with the data of my ipod?

How to delete all of my information on my iphone if the screen doesn't work and it has a passcode?

I have an iphone but dropped it in salt water on beach and its destoryed i got a replacment phone but need to delete all my info before i send it back… But i can't because the screen is destroyed and when i hook it up to my Macbook to hook it up on itunes but it says phone is locked and you have to unlock it to get in it. So how do i delete all my stuff if i can't get in to it Please Help

Can I use my unlocked iPhone 4 with walmart family moble?

I have an iPhone 4 that I originally purchased from AT&T but it got too expensive so I got the phone unlocked and switched to metro pcs. The unlock was successful because when they put the SIM card in at the store everything worked and I've been using it for about 6 months now. Now I'm thinking about switching to walmart family mobile. Can I and do they have micro SIM cards? Also what would I have to do to transfer my metro pcs phone number to walmart family moble?