Turn the phone on with no SIM card and dial 2945#*345# (as if you make an emergency call) if the menu appears (you will be able to select Select Service Provider lock or Network Lock) then it can be unlocked by the code you can get one at e.g. https://www.mobileunlocked.com/lg/h345
If it uses the Device Unlock app (some -T-Mobile phones have this app installed before the purchase) it can be unlocked by this app only - no hidden menu appears, no code will help.
Answers & Comments
Hi Adrian Naranjo,
Turn the phone on with no SIM card and dial 2945#*345# (as if you make an emergency call) if the menu appears (you will be able to select Select Service Provider lock or Network Lock) then it can be unlocked by the code you can get one at e.g. https://www.mobileunlocked.com/lg/h345
If it uses the Device Unlock app (some -T-Mobile phones have this app installed before the purchase) it can be unlocked by this app only - no hidden menu appears, no code will help.
Mostly it needs a code from the company and that is available after you pay out the contract for that service provider