This flashes the modem.bin file... which writes to a separate DevBlock (partition).. won't write to /system, /data, /boot, /cache. I flashed this MA4 modem over my LK7 modem (while running CleanROM v4.5).. works fantastic. I'd recommend backing up your current modem partition (in on TWRP), then flash this... if it doesn't workout better for you, restore your current modem.
I did exactly this last night, and everything went fine. Still experiencing Wifi dropout though. Only solution is to turn off Wifi PSM via the *#0011# menu...but I have to reapply with every reboot. Was hoping the issue would be solved with new modem, but at least I'm getting better wifi upload speeds when it stays connected.
I just installed the newest AT&T modem. After picking "reboot system" in TWRP, I noticed a little flakiness on 4G and WiFi data. Powering the phone down completely and restarting seems to have gotten rid of it. Just posting in case anyone else sees similar stuff.
ssewk2x aka Efpophis
Verizon Fascinate (retired)
AT&T Note II - PAC-man (whatever nightly I managed to flash last), Devil kernel (latest, possibly my own custom build)
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