When you open the stock text messaging app on the G3 and can view all conversations tap the 3 dots to open up the pop down menu. Where u will see things like "Search" and "SIM Card Box", as well as "Settings". Open Settings in the text messaging app and there are options for Notifications, Storage, Text Messaging and Multimedia Messages. I don't know if this will help but under the Text Messaging part when u tap it just displays a Service number. This is the Text Messaging service number your messages are routed thru and(is different than YOUR number) you might need this original (default) number to enter somewhere in the messaging app u want to use.. All I know is I messed with that number and couldn't receive a text until it was fixed. Same thing with Voicemail. Go to your Call Forwarding and the number to your Voicemail is not the same as your number! Again the default number might need to be entered somewhere in the settings on the New App u are trying to use!
My area code is 702 but the number to text and services is a 312 number and voicemail a 619 number. Service Center Address as it's called in Text Message settings.
Good luck.
From my LG G3 on AT&T...
* Another thing if you don't have the box checked by Automatically retrieve MMS then your phone blocks and kind of 3rd party pictures or videos from being automatically downloaded when u open the message which is a defense against the "Stagefright" type virus. And in MMS or Multimedia settings should be an option that says "Creation Mode" which has 3 choices, Restricted, Warning and Free!
Make sure this is set to FREE
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