So I paid for my phone to be unlocked by doctorsim. So far theyve been very responsive and helpful. They've indicated that the 8 plus cannot be unlocked via IMEI, so they sent me UMS (unlock my sim) sticker thing for free. It came in the mail, its like a small piece of thin plastic with some contacts on it, and it gets placed under your sim card, which makes the sim card connect to it and THEN into the phone. This whole thing was never made clear by anyone so I decided to explain it. Now, The SIM I have I bought from Straight Talk, for an unlocked verizon iphone 6. It works perfectly with that phone. However, the Iphone 8 plus I inherited is from AT&T, or at least thats the SIM card that was left in it. As per the instructions I inserted the SIM I had with the UMS into the iphone 8 plus, and was presented a menu, which was overlaying the iphone activation screen. I chose to edit the ICCID and put in the code provided on the website. I hit send and the screen simply disappeared and i finished setting up the iphone. It said "No Service". I restarted the phone, same deal. So I reset the phone completely while leaving the SIM and UMS in it, and when it came time to activate the phone the UMS menu did not come up, and now it is saying SIM not supported. The iPhone 8 Plus is not blacklisted or icloud locked, and Find My iPhone is turned off. So did I do something wrong or do I need to get an AT&T compatible SIM from straight talk or what? If anyone knows how to fix this please let me know.