Well srboromir, that's a little odd that just your phone is getting that error, but I want to help. I'm curious, can you try your SIM in one of the other phones to see if this same thing happens with the 2G connection?
As for the phone overheating, is this happening when you're using certain apps? I just wanna get a feel for how to help you out with this before jumping to a reset. Keep me posted. Thanks
I swapped out SIM cards between my phone and another family member's. Would've been simple if I just needed a new SIM card, but alas, the problem was still present on my phone with a different SIM in it. And my SIM in the other phone worked correctly.
And as for the heat issue, 3D games like Fallout Shelter would heat it, but so does any data streaming, Pandora for instance. Or if specific apps were installed and running in the back (had to uninstall every Amazon app I had)
The phone would also heat up if I was driving/riding in a car, even if the phone was locked and idle, and in my pocket/ center console.
I will admit that the moisture indicator in the battery compartment has turned pink, this was because to overcome the heating issue, I have had to set the phone on a CPU heatsink, and one liquid cooling heatsink leaked and I had to dry the phone out.
Thanks for testing the SIM card out. Since 2G works in another phone, that let's us know it's something going on with the L90. You could try uninstalling 3rd party apps to see if we can narrow down one of them as the culprit. We may be looking at a reset as the last option to fix the 2G issue.
It's normal for the phone to get warm when using application. It can also heat up a bit more if you're doing a lot of streaming for a long period of time. If that's not the case and is just sitting idle, that's a different story. If possible, testing another battery is an option to see if the overheating stops. Moisture could have some influence on the phone behaving like this, but it's hard to tell. (Liquid exposure can do some strange things.) Testing another battery can help us with this theory.
Depending on if you have handset protection, the next options would either be replacing it through filing a claim, or seeing if you can get LG to repair it. Issues like this can be a little tricky to handle, but those are my thoughts on how we can go about resolving this.