Not so many comments. OK I did some research on Youtube and reason is very clear. It is because of the antenna. More precisely the lack of the antenna.
Look at the inside picture of LG G2 and Samsung GS4. Ther is nothing between the contacts. Well would it be so expensive?
Anyway I will to fix it later. Firstly I need the appropriate tools for opening the back cover without any damage. You too can find few videos how to disassemble the phone.
I suggest to watch this in any case although the quality is not HD.
If anyone did this mod don't hesitate to share the result.
Warning! If you don't have enough experience in repairing electric devices do not try to do it alone.