What does #0111*NETWORKCODE accomplish?
First off, my apologies if I am in error about GSM functioning on my phone.
I will explain what I've done with my Sprint S4 mini and maybe you/someone can tell what is happening. But this is why I thought GSM was/is working on my phone, until supermaxkato questioned this. (Note: I am not a developer.)
My S4 mini is active with Sprint. If I put a GSM SIM in it, of course it does nothing. Try to make a phone call and I get an automated message that it cannot be completed. But after doing the following, I can make calls, send texts, use mobile data.
I powered on with GSM SIM in phone. Entered #0111*NETWORKCODE for my phone in the dialer and hit call button. After this voice, text, data work. However, phone shows "Invalid SIM" in the notifications and the calls and texts come from my Sprint phone vs. the number associated with my GSM SIM. (I didn't realize this until testing last night.)
So did the code just make it so the SIM tray ignores the GSM SIM and functions on Sprint network? (again.. before entering the codes, no calling/texting/data worked with GSM SIM in the phone)
Same results on 2 activated Galaxy phones. Unsuccessful on non-activated S4 Mini.
I am not tech savvy but if anyone wants me to check something on my phone, I will try to get you the information. (I do not have a rooted/modified phone.)
Again, sorry for my mistaken report of success. In retrospect, I should have known it couldn't be that easy.
(Earlier this year, I WAS told by a developer in Colorado that there has been limited success with Sprint S4 minis being unlocked for GSM both internationally and domestic. And a Sprint rep recently told me that this phone can be unlocked internationally for GSM, although I see that it is not on their list of unlockable phones.)