1. I have Stock ROM (4.4.2) and last firmware installed and root.
2. Download the files you will need HERE install QPST and QXDM, u can get the drivers intalling HTC Sync Manager from HTC webpage.
3. Dowload Terminal Emulator from the market.
4. Open the terminal emulator and put the code on @regspy guide HERE
5. Put your phone in CDMA mode.
6. Open your phone dialer and type ##3424# (an image should be appear on your phone screen).
7. Connect the phone to your PC.
8. Go to start, all programs, QSPST, open QPST configuration (as admin).
9. On QPST configuration go to Ports and click on add new port.
10. Open device manager, go to PORTS and check what port are using your phone.
11. On QPST configuration fill the PORT and PORT LABEL, PORT LABEL should be HTC Diagnostic Device or something like that, now click OK.
12. Now open QXDM.exe (as admin).
13. Go to options, communications.
14. On TARGET PORT select your HTC phone and click ok.
15. On VIEW select NV Bowser.
16. Find +6828 click read button and backup the stock value on a paper, txt file, etc just in case.
17. Repace Both values with 524356 and click WRITE.
18. Do the same with +6829, use the same value.
19. Reboot and enjoy!!
20. Put the phone in Global Mode.
Stock GSM Values (thanks to @BobbySteel):