[G3 Q&A, Help & Troubleshooting] BakedTator:
OK people, it took a good bit of time to do this and the help of a few devs to figure this out (not to mention it took me about a month and I had to completely brick an AS990 to finally get this) to get this working right!

After days of testing, I'm happy to say everything works as it should!

I know there is no development for the AS990 and as far as I (and the others that helped me) know, there is no way to get and custom recovery on the AS990 except for this guide!

Disclaimer : I am not responsible for what you do to your phone! If you brick it doing this, you must not have followed these steps right! Please know this will void your warranty!

So here it is!

The first thing you need to do is the obvious, root your device! I used iroot to root the AS990! I will post the link to it once I find it but a quick Google search should do you some good here.

Next thing I did was the crazy part! I used this link and followed its instructions to the letter and be sure to backup you apn-config.xml located in /system/etc/ and use the change apn app from the play store and write down all the info for your apns before you continue (this is a must to get data, including lte and mms!)...don't skip anything this guide says...you will turn your AS990 into an LS990 following this link...Again, follow the instructions to the letter!!! Don't cry to me if you don't follow it exactly!!! I have used this method on 2 AS990's and 2 US990's!!! (Yes, this does work for the US990 as well but I don't know if you will get lte as my uscc sims are not active).

https://m.reddit.com/r/LGG3/comments/3if357/lg_g3_as990_to_ls990/

After you do this you will not have service while on stock sprint rom, but don't fear, Tator is here!

Now that you are on stock sprint with your AS990, you again, need root...use whatever rooting method you want for sprint...I used the one click root for lg g3. Now that you have root use flashify to download and flash twrp for the LS990. After you have twrp working, you will want to pull the modem.bin from the AS990 tot using the tot extractor. After you pull this file from the tot, you will rename it to modem.img.

Link for the AS990 tot that I used : http://xdaforums.com/lg-g3/general/lg-g3-as990-firmware-as99010a-t3183928/post62444120#post62444120

I used the windows cmd prompt and did the "ren modem.bin modem.img" (without quotes) to rename the file after I extracted it.

Link for the tot extractor : http://xdaforums.com/showthread.php?t=2600575

Then move the modem.img to the internal sdcard of the phone. Then using terminal emulator, I did the following

su

dd if=/sdcard/modem.img of=/dev/block/platform/msm__sdcc.1/by-name/modem

That will flash your stock AS990 modem back on the phone (which is needed so everything works right).

After you have done all this bs, you are free to flash any aosp LS990 rom you would like to run! (I have only tested aosp because its all I run on my phone) just be sure to move your apn-config.xml to /system/etc and then enter your apn info you had written down (you may have to use change apn from the play store to do this depending on what rom you have flashed) and you should be good to go!

I will edit this and organize it more later because I'm pressed for time right now! I will also give credit to those who helped me through this process! Any questions, please post here and I will do my best to help anyone who needs it...I know this is poorly written for now but again, I'm pressed for time! If there is anything you don't understand about this how to, please be patient with me as I make revisions throughout the day!

Credits : bender_007

jorapi

the creators of the tools used to do this

and myself

If I forgot anyone, please inform me. I will always give proper credit where its due!!!