If you have never sent a text message on this phone, it is possible that it contains an incorrect message center number or MCN. The MCN is usually set automatically as soon as you insert a SIM card into a GSM device. For CDMA telephones this is usually pre-set by the courier. In case this has never happened, you can manually check the MCN by following these steps:
Open your Messaging app.
Tap More Settings (three-dot icon) in the upper right corner.
Tap More Settings.
Tap Text Messages.
Tap Message Center.
If you do not know the correct MCN, ask your provider.
My significant other and I are having the same issues. S8 Plus from AT&T (G955U) from Best Buy. They activated it on the AT&T network. I then found out that the device we both have are the unlocked version. We can send to an iPhone user, but cannot send texts to an Android user. This is stupid.
My husband and I got phones at the same time, his phone had the problem, mine did not. We went to ATT and after updating the software and doing some random stuff which did not help, the guy simply gave a new sim card and it worked! So it could be an issue with the older sim cards. Why I did not have that problem? - my guess is b/c I got a new sim card when we were getting the phones, while my husband used his old one.
I've been having sending and receiving text messages also. I also bought the unlocked version of the S8. Samsung needs to figure this out because like everyone else, i've missed so many important text messages. It is ridiculous that they still have not come up with a solution for it.
You mentioned having an unlocked version, but which carrier are you using? Have you had a chance to try any of the suggestions found on this thread?
i'm using the unlocked version through tmobile. i've tried all of them, i've even tried samsung help support; they resetted the messenger apps, even touchwiz app, cleared out the cache and memory..... the issue is still there. the person I chatted with said the issue was resolved... it was not.
My issue is when i use FaceBook. When i watch the videos. My message que will hold message for over 6hours before sending. Ill clear out cashe. On fb and messanger, reboot and it still will hold.. this problem started with the note 7. Also. I have not do a full reset of the note. But did anyone find the true problem.
I also had some text msg'ing issues with sending and followed instructions to clear the cache partition. I also entered safe mode (only allowed it to load before i changed my mind and exited) and...
NOW ALL OF MY CONFIGURATIONS HAVE BEEN CHANGED. wtf???
-- Settings background (was set to dark)
only change was the cache partition; no apps were modified. safe mode was exited by both restart and by boot menu in "normal" mode.