[Nexus 5 General] Simaramis:
For anyone still wanting Spring Service with a recent Custom Rom-IT CAN WORK

edit Nov 2019: likely this works better to get LTE data on Sprint devices working:

https://xdaforums.com/showpost.php?p=80742787&postcount=705

TL/DR:

Eventually it's possible to get Sprint working with an older device and a more recent rom. Not sure exactly what does it though. Note: I was unable to locate the sprint.zip until just now, it's why I am posting here. I would probably recommend flashing that instead of the Freedompop_APN_fix.zip.

The following finally ended up giving me LTE on Sprint NEXUS 5 HH on a Android Pie custom rom AOSIP 6.6. I did similar thing years ago with my LS-980 LG G2 device getting Nougat to work.

0. Re-partitioned system partition to facilitate Pie Rom. Might have done this after 1. below not sure anymore.

1. went back to stock, did PRL reset, this gave me LTE on KitKat.

2. Rooted and installed TWRP 3.2.3, did full nandroid backup of the stock rom, and then flashed a stock-based Marshmallow custom rom., this kept LTE. kept this bare and without Gapps. Everything worked. Did a full Nandroid backup of this also in recovery.

3. Dirty flashed Pie Rom zip from TWRP. This showed Sprint service for telephony, and bars on status bar, but neither worked, no data, no texts, no calls in or out.

----I have a hunch 4.-12. can be skipped and go straight to 13.----

4. installed Magisk, installed SELinux mode changer, changed to permissive, installed busybox, installed SystemAppMover, Installed APNBackup and made it system app with SystemAppMover, changed buildprop ro.carrier=spr (instead of unknown), rebooted.

5. This didn't do much, except now it said there was no sim card. Opened APN Backup and restored APNs I had backed up before in the Marshmallow Rom. Re-booted, no change.

6. Repeatedly reset data&wifi&bluetooth, tried update PRL and Update Profile in Settings/Network/MobileNetwork/Advanced/CarrierSettings which gave errors. Re-booted, no improvement.

7. Took out and re-inserted sim. Now it read the Sim card again (did not say NO SIM), but no improvement, meaning no data, no telephony.

8. Fiddled arount in the *#*#4636#*#* Phone information Menu, changing the mode. Here it would not see my phone number on Sim. No improvement.

9. Flashed MVNOBusbee.zip and PrlProfileFix.zip from threads below. Tried all different modes, i.e. Sprint, Ting, Virgin. No improvement.

10. restored the efs partition from the Marshmallow Nandroid, rebooted, no improvement.

11. Went back into TWRP and flashed the Freedompop_APNs_fix.zip. Rebooted, no improvement. NOTE: may be better to flash sprint.zip at post 136 of this thread.

12. tried PRL and profile update again, which gave errors. Reset Mobile, Bluetooth, Wifi again. no Improvement.

13. Re-booted, no improvement, went into the test menu *#*#4636#*#* and changed the mode around again. it now showed my phone number under sim, and it showed Freedompop as provider, but stated Data Service: disconnected. So I moved around and tried Global, LTE/CDMA/UMTS, EvDO only, basically switched back and forth between the options that showed something under Current Network: (Freedompop in my case, even though that's just because of the zip I flashed, my MVNO is not FP). I did this a few times, and eventually one of them gave me 3G. Then I went and and did profile update under Settings/Network/MobileNetwork/Advanced/CarrierSettings and this did not give an error, it took a short while, and poof I had LTE signal popping up.

That's it, no clear method. But eventually it worked. Funny thing is that LTE and 3G are about the same speed LOL.

The key seems to be flashing the Freedompop_APN_fix.zip. There is also a sprint.zip that I had trouble finding at the thread listed under main thread below. I had trouble finding that one but it is actually downloadable from a post in that thread on page 14.

All relevant zips are at post 135, unless you need to try the freedompop apn fix.

Credit goes to the following threads:

Merudo's Freedompop APN fix: https://xdaforums.com/showthread.php?t=2798619

PRLProfileFix.zip-https://xdaforums.com/showpost.php?p=58118888&postcount=46

MVNOBuzbee.zip-https://xdaforums.com/showpost.php?p=65917850&postcount=30

Getting CDMA networks to work on Nougat Roms:

https://xdaforums.com/google-nexus-5/general/getting-cdma-networks-to-nougat-roms-t3534679