Good news is that SPR L720 works on OMH very well with data. I received a few phones last week which were shipped on 4.3 OTA. Rooted, flashed phil's recovery and updated to NAE 4.4 modem.tar, flashed rooted stock TW NAE 4.4 flashable ROM.zip from recovery and it reads any RUIM. Have also tested other international CDMA SIM cards on this baked tutorial.
Chinese tutorial:- http://www.cdmamod.com/thread-1840-1-1.html
the files:- http://pan.baidu.com/s/1hqsUCJU
Note 1:- that GSM unlocking requires MDC modem, s4 unlocker and such, and that hidden menu may not be operable on 4.3/4.4 so please make sure its done before this procedure. The chinese tutorial states that a stock MK2 odin file is used, and then the 4.4 zip and the NAE modem, but i have not updated to 4.3 bootloader.
Note 2:- OMH/GSM/NV mode (3 networks as called in China) also works on MDC base and CM roms.
*Please use your favourite CDMA software to make the phone RUIM only/RUIM if avail before proceeding to this topic.
*GSM usage by this method is under development. The entire tutorial is experimental and aimed towards achieving stock like performance.