[Moto E5 Questions & Answers] AeonFlux1603:
I have found at least one constant regarding the Sprint, Boost & Virgin Mobile Moto E4 (xt1766) and Moto E5 Play (xt1921-5). Well, two constants actually.

1. These carrier branded devices ship with a pre-installed Sprint UICC (SIM card). When unboxing the device for the very first time, it is crucial to remove the Sprint UICC prior to first boot and initial setup. Booting the device for the first time with the Sprint UICC installed, the device becomes locked to the CDMA network identified by the 20-digit ICCID. At this phase, GSM support is disabled and the device is configured to operate only on the network to which it was originally branded. (On the xt1766 Moto E4, this network lock is nearly impossible to overcome or bypass by user-end mod or exploit. It appears that booting the device initially with the pre-installed Sprint UICC permanently locks the device to its branded network. The xt1921-5 Moto E5 Play is strikingly similar to its E4 predecessor in this regard);

2. If either of these carrier branded devices is booted initially, with the pre-installed Sprint UICC removed, there are some user-end mods and exploits available to enable full GSM network support for domestic and international GSM service providers. On the Moto E4 xt1766, GSM support can be enabled by simply unlocking the bootloader and installing the initial firmware package available for the xt1766, which included a default option in Settings>Mobile Networks to add new APN configurations. (Here, it appears that firmware build NCQS26.69-64-8 engendered an interesting restriction -- the inability to downgrade baseband radio firmware to a previous version. This restriction was presumably put in place by the 64-8 maintenance OTA to prevent downgrading to a baseband firmware version that permitted GSM support options and/or the adding of new APN configs. Interestingly, the 64-8 baseband downgrading restriction has no force or affect if you booted your device initially WITHOUT the Sprint UICC installed. On the xt1921-5 Moto E5 Play, full GSM functionality and support can be attained simply by rooting the stock Android 8.0.0 Oreo OS and adding an option in Mobile Settings to add a new APN. The SCRTN menu should be initiated to commence a telephony reset after your GSM SIM is installed (##72786# or ##27263#). The *#*#4636#*#* radio menu can be used to set your preferred network mode to GSM/LTE auto_PRL and to change your radio band preferences. (The MSL/SPN code is very handy if you want to use the ##3282# menu to tweak LTE Priority Band settings, carrier aggregation preferences, etc.) A good old-fashioned root file manager can be user to rewrite your stock apns-config.xml, eri.xml, etc. With Moto E5 Play, I've had good results by flashing a Treble supported LineageOS 15.1 unofficial system image for GSM support. Again, I emphasize that whether you are using the Moto E4 SPerry or the Moto E5 Play James, and you are wanting GSM support for domestic or international GSM providers, it is imperative that you never boot the device for the very first time with the pre-installed Sprint UICC. With older Moto devices, such as the Sprint compatible Moto E2 2015 and Moto G3 2015, Sprint (and its subsidiaries) implemented a much more arcane methodology for network locking -- sensitive partition encryption embedding. To Sprint's credit, four years after their respective manufacturing dates, the best hackers, modders and developers in the entire technological world have yet to bypass or exploit these network restrictions. It simply cannot be done. In a nutshell, Sprint network locked these and similar Moto devices by embedding encrypted code to at least three protected and sensitive device partitions -- /pds, /hob & /dhob. This network restriction protocol was also brutally simplistic -- tamper with one or more of these protected partitions, you run the dire risk of bricking your device beyond any chance of repair. Hey, I for one am glad of this new UICC/ICCID dependent methodology.