What I found to be the fix is to disable the "Smart Network Switch" option, then turn off wifi and go on the internet and load any web page. This usually would kick start the text messages to be sent to my phone. Once you disable the smart switch, you can keep wifi on all the time and you will not have any problems with texts, MMS or calls.
DISABLE SMART NETWORK SWITCH = WORKING TEXT MESSAGES!!!!
Please let me know if this fix works, thanks.
I don't know who else has been having this issue, but there are times where I would not be able to send or receive text messages until I restarted my phone. I finally narrowed it down to the main culprit, which is "Smart Network Switch" under the "Wifi" settings. The problem occurs if you are actively connected to wifi and you turn the screen off. Your GS5 is in sleep mode now but still has wifi connected. When the "Smart Network Switch" is off there is no problem, but when it is on it prevents text messages, phone calls and MMS. It happens either the phone is charging or not charging.