[Samsung Galaxy S8 Questions and Answers] tryn722:
I have been using a couple services for unlocking my S8 devices that I buy and sell. They include samsungsimunlock*com ….. this is my first goto because they are cheap and fast, they also will refund money for invalid codes. The ones that say permanently unlocked but aren't. They have told me at times that the security level was higher usually costing $26 instead of the usual $13. I have used unlockbase*com which I think was pretty good and cost about $17-20. I recently had some trouble with a couple network codes for 2 SM-G950U, one Boost and one T-Mobile. I used OnlineUnlocks*com for a remote unlock, which was my first experience with someone outside having remote access to my computer. They spent 4 hours flashing and unlocking my Boost S8 and charged me 29.99. When it came to the T-Mobile, all estimates put it over $50, which normally I get a code and a app, to unlock T-Mobile S8's for $13 through Samsungsimunlocks. After a night of research and flashing, I finally found another member here who was helpful. I'm not sure if I'm allowed to mention them or the cost of the unlock but it was cheaper than all the companies I normally use. My experience tells me that there is some new security issues are related to the Bootloader 3. I don't seem to have the correct firmware on the device that I had hoped for, and it is currently on the Sprint network and obviously has somehow loaded all the Sprint garbage related to original carrier firmware. Unusual from my experience.

What I normally do is keep the device on whatever firmware it has through the unlocking process unless I run into issues with the phone actually being unlocked but still not recognized by a network. I have had issues with all the major carriers at one point or another; but, the exception is Verizon. Cudos to them for their current unlock status. The weird thing to me is, one device from "carrier 1" will unlock with no issues while the same SM-G950U will have issues with "carrier 1" days or weeks later. Carrier 1 is whatever carrier you can think of with the exception still being Verizon. The one obvious sign of trouble is when it is unlocked, yet in settings, you wont find UCCID unlock under software updates. Firmware?? The overall worst carrier to unlock through a third party, for me, was an Xfinity Note 8. Again the issue appeared to be the device stating, "unlocked to any network", but not recognizing other SIM cards. For whatever reason, it seems to be firmware related. My best advice is to get your devices unlocked through your carrier first. Then try a third party. When that is an issue, bring it here and research your phone. Two things you want to know right away. … Exact model number and iemi (do not post your iemi), and Build number. Make sure to have those available when asking for advise from other members. People more knowledgeable than me know what to look for. As many as I have bought and sold, I just don't have the daily experience to know what to look for and do. I should keep notes but get a one track mind when I'm frustrated over a device.

***Update*** I recieved an email today explaining that the new owner of Samsungsimunlocks has been put into a situation where their current codes are useless. It's recommended that if you try that service, that you send them a message first to avoid wasting your time. He/they were very professional and honest about the situation.