mobile

Hi

I have a Sprint Galaxy S4 and I try desperately to put sim cards from other carriers and foreign (French) sim cards but nothing works. I always get a guy's voice saying something like "your account has not been authorized for this type of call"

I have done all the possible "unlocking" of the phone, but I'm not sure what it really means:
-I have made the procedure where you get to the hidden "service menu" type "debug screen>network lock>..." (btw my SHA256 was already off, whatever it means. No change here.) (I had to downgrade the radio)
-I have successfully done what was indicate in this thread http://forum.xda-developers.com/show....php?t=2415587 with the "unlock" software, at that point the phone was not saying "invalid sim card" anymore (thanks, Autoprime!)
-I have rooted my phone, clean installed a new rom (I put negalite, quite cool)
-I have obtained my unlock code from Sprint, but I've never been able to use it. If I type ##[CODE]# I get to a menu where I prefer not touch anything

I don't know how to make sure that my phone is able to support GSM. How can I be sure? It has a SIM card slot but I'm not sure what that means (and on Sprint the phone works without the sim card). I'm going to Singapore in one month and I would have liked to use local sim cards.

That's a lot of questions! But I'm really lost here, and I don't see any post that seem to help me...

Thanks
Raph