My dad had the same problem with his Galaxy 5 Grand Prime. He went through three SIM cards and got the same "invalid SIM" message each time. Finally Samsung sent him a new phone and that one seems to be working.
According to the person he spoke with at Samsung, the SIM card thing is a "common issue."
But your phone isn't a Samsung so apparently it's a problem that a lot of phones have. My LG had that issue once as well.
Thanks for letting me know that Gabby !
At least that gives me confidence my replacement phone should work okay, after all, what are the odds I would get 2 defective phones in a row especially when the replacement phone is from a different seller.
I just got a message from the ebay reseller a few minutes ago not only agreeing to refund me after the defective phone is returned, but gave me a pre-paid return label to print out so it won't cost me anything to return it.
I ordered another Nokia Lumia 1520 from an Amazon seller as they ship fast, I ordered it Saturday and it will be here Monday !
The ATT store I went to tried more than one sim so they said it had to be a defective phone.
While they were working on it the employee also opened the tray next to sim tray saying what is this ?, oh, it's a memory card.
Then a few minutes later they looked on the floor and said "I thought I dropped something", but couldn't find anything. I was so focused on hoping they could get my phone to work I didn't think much about it.
Then when I got home and was going to take my memory card out knowing I had to send the phone back, it wasn't there, later that day after my wife got home I used her phone to call them and tell them what happened the regional manger who happened to answer the phone looked for it and when he couldn't find it agreed to make up for the cost of replacing it with agreeing to give me a $25 credit in my GoPhone account (the memory card was $25.35) so they were decent to work with.
Now as far as some of the ATT people I talked to they said a defective sim reader in a brand new phone can happen, but they said it's not real common for new phones, so I guess that just happened to be their experience so far at that location.
Maybe that Samsung model had a design flaw that made it more common than what normally might be expected.