In an attempt to make this guide short and comprehensive and also to prevent the completely uninitiated from doing something stupid, I'm going to skip babysteps like <power on your coputer> or <browse to x folder and doubleclick on y>
I start this assuming anyone following it has a basic understanding of what they're doing, what ADB is and also of the risks that come with messing with their device.
This guide will show you how to alter the default baseband frequencies of your qualcomm-based device, augmenting them so that (theoretically) it should work more like a global phone.
Those with an international version of the OPO can still follow this guide, if only to check your unlocked bands against those of your fellow chinese OPO owners. I'm of the opinion that even the international version lacks a few GSM/WCDMA bands, so no harm in trying to unlock some aditional ones.
This guide will, however, NOT UNLOCK ADITIONAL LTE BANDS. At least not for now. It will be updated if and when someone discovers a way to tamper with the LTE bands.
1. Download this archive containing all the necessary files and extract it wherever you please.
2. Enable Android Debugging on your phone and connect it to your computer, making sure MTP and PTP are not enabled in Storage > USB computer connection
3. Open up ADB and type the following:
setprop sys.usb.config diag,adb
4. Launch Device Manager and look for the Other Devices expandable menu.
5. Right click on the first device listed under that menu (the first of the two A0001 devices listed there) and choose Update Driver Software, Browse my computer for driver software, Let me pick from a list of device drivers on my computer, Show All Drivers, Have Disk and Browse
6. Browse to where you extracted OPO SPECIFIC QUALCOMM BAND UNLOCKER and locate the OPO Diagnostics Driver folder; Inside you will find 32bit and 64bit versions, pick the one relevant to you and inside you will find an .inf file that you will Open. Accept any warning messages that might pop up and let the installation of the driver complete.
7. Once everything is done installing, under Modems in Device Manager you will find HTC USB Modem. Rightclick and select Properties; In the Modem tab in the top left corner you will see Port: COM<number>. Remember that COM<number> or write it down or simply leave the window open for future reference.
8. Open the OPO SPECIFIC QUALCOMM BAND UNLOCKER folder, locate and install QPST 2.7.411 inside QPST > QPST v2.7 Build 4.11
9. Open QPST Configuration, go to the Ports tab, Add New Port (right bottom corner); In the Port field type in the COM<number> you wrote down/remembered from step 7 and in Port Label type OPO and finally click OK (left bottom corner). If you've followed all the steps correctly until here, you should be able to see this in the Active Phones tab:
10. Locate and launch RF_NV_Manager.exe in the bin folder of the QPST installation directory (normally C:\Program Files (x86)\Qualcomm\QPST\bin)
11. Once you have RF_NV_Manager.exe open, click on Setting > Comport and select COM<number> from the dropdown menu and click OK; Go to File (top right corner) and select Read from Phone and let it finish.
12. Scroll down and click on line 1877 (NV_RF_BC_CONFIG_I); Copy the number displayed on the right-hand side field (the one next to < unsigned 8 bytes > Band Class(s) Supported >)
13. Locate and open mzTool_1.2.1a.exe inside OPO SPECIFIC QUALCOMM BAND UNLOCKER; select Decimal under Input Radix (top left side); Paste the number you copied in step 12 into the Decimal field under RF BC Config. You should now see your currently available bands in the Bit Information field underneath. It should look similar to this:
14. Go to Band Performance (NV Value) tab and check all the GSM and WCDMA bands; Copy the number in the Decimal field under RF BC Config (2,307,813,334,319,039,360); Copy it into a text editor and remove the ","
15. Go back to RF NV Manager and paste the clean number (2307813334319039360) into the number field next to < unsigned 8 bytes > Band Class(s) > --- if you paste the number with commas or brackets instead of just the number, you're an idiot.
16. Press WRITE NV then go to File and select Write Changed NV Items To Phone; Wait 23 seconds (because I like arbitrary waiting times), disable Android Debugging on your phone, unplug it and reboot your device; Once it comes back on, it might take a few seconds for it to acquire signal so don't panic.
NEW LTE UNLOCKING GUIDE
Courtesy of @Albirew
The only real way to know if the whole thing got applied is to do steps 1 through 13 again (obviously skipping installations) or if you are in an area where you previously had bad or no reception.
I've tested this on my 64GB Chinese OPO running stock rooted CM11S. Everything seems to work properly radio-wise, no worse than before. I'll have to travel a bit around to see if i get better or worse reception.
I'll edit this thread with any relevant information if any becomes available in the future or if anyone feels something is missing.
Thanks to @BlackSoulxxx for his original work with the Qualcomm baseband software and for the modified OPO Drivers
Thanks to @olokos for his original tutorial
Thanks to @Glatzi for bringing the original thread to my attention
Thanks to @fards for finding the diagnostics command that made all this possible
Thanks to @Albirew for writing an extensive LTE tutorial