It seems like T-Mobile dropped the ball with LG Phones recently. Both of our LG Phone on T-Mobile got the error that the LG IMS service kept failing. At first I thought it was just something bad with my phone and I did a factory reset which did nothing. Later I learned that my wife's phone was also having the same issue. So I looked up the error and T-mobile and several pages popped up to explain that this issue just happened.

Seems that T-mobile was pushing out an update across their network that affected LG phones. Of course it does not help that LG has gotten out of of the cell phone market. I am going to guess that is why T-Mobile did not notice that the change was going to affect people with LG phones.

At any rate a fix is forth coming and there is a fix that you can do to stop the error from popping up although that fix is not an official fix. Still it did solve the issue on both our phones.