I am currently on my second G2, a refurbished "like new" model. I've only had it a few weeks and I'm ready to throw it in the trash. First phone had a headphone jack issue that caused the mic to stop working. It would act like the headphones themselves had a short and any tiny movement would make the plug icon (the animation of the plug being plugged in) blink on. After a few days it wouldn't register a set of headphones at all, and to top it off the microphone quit working eventually, I could hear people but they couldn't hear me on calls. Fast forward to a few weeks later. Got the "new" phone and I have already had to do 3 factory resets to get it to send picture messages. I've since found out they know about the issue, but have no plans to fix it until SEPTEMBER!!! Needless to say this phone is doing the exact same thing with the headphone jack. Knowing I'm going to be stuck with this piece of !#$# phone till I can upgrade I've had to spend the money and get wireless ear buds to be able to still hear my music. (So much for that nice expensive pair of Beats by Dre I spent all that money on.) And after reading numerous discussion threads support here talks to us like we're all stupid. "Have you tried using the headphone in another device?" Why yes, I did, when a $400 dollar pair of headphones appears to quit working you tend to do some checking around....
For the audio issue, are you using a special music program that you installed? If so, uninstall it and try another.
The MMS issue I think is being felt by many, and some patch will be required. But two devices having earphone jack problems seems suspicious... unless you are cycling the jack a lot by plugging and unplugging phones or buds a lot.
The headphone problem is a known issue as well. You can google LG G2 Headphone jack and see many other complaints. I use my headphones at work, while it is manual labor, it's nothing too extreme. Usually once I plug the headphones in they stay plugged in for about 5 and a half hours. I may remove the ear buds, but I always leave it plugged in and playing Spotify or Pandora. It's broken from just day to day usage. And its happened to 2 phones back to back.