MC vs EM is the form factor. Most devices are USB devices that the USB interface on MiniPCIe. SIM support works by wiring pins from the SIM card to standard pins on the PCIe interface. 74xx models use USB3, but some boards don't support this. As a workaround, you can tape over USB3 pins, forcing the device to USB2.
- EM7455
- MC7455
- MC7354
Specific Sprint SIM cards can only activate specific IMEI ranges. Common SIM cards probably won't work with an LTE modem. BestCellular sells specialized Sprint SIM cards and has a Sprint SIM card compatibilty matrix. Searching their site also finds compatible cards. End-of-life cards work fine. Remember to get the right size card or an adapter.
https://github.com/0ki/mikrotik-tools
base-files - 191-r7360+111-e15565a01c
busybox - 1.28.4-2
dnsmasq - 2.80test2-4
dropbear - 2017.75-6
firewall - 2018-07-02-72684e5b-1
fstools - 2018-05-23-dd02dad3-1
fwtool - 1
glib2 - 2.56.1-1
hostapd-common - 2018-05-21-62566bc2-4
ip6tables - 1.6.2-2
iptables - 1.6.2-2
iw - 4.14-1
iwinfo - 2018-05-18-e59f9253-1
jshn - 2018-06-07-3c1b33b7-2
jsonfilter - 2018-02-04-c7e938d6-1
kernel - 4.9.111-1-3ac64a7e0cff1e878d6c40ac7e57d40b
kmod-ath - 4.9.111+2017-11-01-9
kmod-ath9k - 4.9.111+2017-11-01-9
kmod-ath9k-common - 4.9.111+2017-11-01-9
kmod-cfg80211 - 4.9.111+2017-11-01-9
kmod-gpio-button-hotplug - 4.9.111-2
kmod-ip6tables - 4.9.111-1
kmod-ipt-conntrack - 4.9.111-1
kmod-ipt-core - 4.9.111-1
kmod-ipt-nat - 4.9.111-1
kmod-ledtrig-gpio - 4.9.111-1
kmod-lib-crc-ccitt - 4.9.111-1
kmod-mac80211 - 4.9.111+2017-11-01-9
kmod-mii - 4.9.111-1
kmod-nf-conntrack - 4.9.111-1
kmod-nf-conntrack6 - 4.9.111-1
kmod-nf-ipt - 4.9.111-1
kmod-nf-ipt6 - 4.9.111-1
kmod-nf-nat - 4.9.111-1
kmod-nf-reject - 4.9.111-1
kmod-nf-reject6 - 4.9.111-1
kmod-nls-base - 4.9.111-1
kmod-ppp - 4.9.111-1
kmod-pppoe - 4.9.111-1
kmod-pppox - 4.9.111-1
kmod-slhc - 4.9.111-1
kmod-usb-core - 4.9.111-1
kmod-usb-ehci - 4.9.111-1
kmod-usb-net - 4.9.111-1
kmod-usb-net-cdc-mbim - 4.9.111-1
kmod-usb-net-cdc-ncm - 4.9.111-1
kmod-usb-net-qmi-wwan - 4.9.111-1
kmod-usb-net-sierrawireless - 4.9.111-1
kmod-usb-ohci - 4.9.111-1
kmod-usb-serial - 4.9.111-1
kmod-usb-serial-qualcomm - 4.9.111-1
kmod-usb-serial-sierrawireless - 4.9.111-1
kmod-usb-serial-wwan - 4.9.111-1
kmod-usb-wdm - 4.9.111-1
kmod-usb2 - 4.9.111-1
libattr - 20170915-1
libblobmsg-json - 2018-06-07-3c1b33b7-2
libc - 1.1.19-1
libffi - 3.2.1-3
libgcc - 7.3.0-1
libip4tc - 1.6.2-2
libip6tc - 1.6.2-2
libiwinfo - 2018-05-18-e59f9253-1
libjson-c - 0.12.1-1
libjson-script - 2018-06-07-3c1b33b7-2
libmbim - 1.16.0-1
libncurses - 6.1-1
libnl-tiny - 0.1-5
libpthread - 1.1.19-1
libqmi - 1.20.0-1
librt - 1.1.19-1
libubox - 2018-06-07-3c1b33b7-2
libubus - 2018-01-16-5bae22eb-1
libuci - 2018-03-24-5d2bf09e-1
libuclient - 2017-11-02-4b87d831-1
libusb-1.0 - 1.0.22-1
libxtables - 1.6.2-2
logd - 2018-02-14-128bc35f-2
mtd - 21
netifd - 2018-07-11-5cf79759-1
odhcp6c - 2018-06-20-b99c1f63-13
odhcpd-ipv6only - 1.9-1
openwrt-keyring - 2018-05-18-103a32e9-1
opkg - 2017-12-07-3b417b9f-2
ppp - 2.4.7-12
ppp-mod-pppoe - 2.4.7-12
procd - 2018-07-05-a0372ac0-1
rbcfg - 2
rssileds - 0.2-1
screen - 4.6.2-1
swconfig - 11
terminfo - 6.1-1
ubi-utils - 2.0.2-1
uboot-envtools - 2018.03-1
ubox - 2018-02-14-128bc35f-2
ubus - 2018-01-16-5bae22eb-1
ubusd - 2018-01-16-5bae22eb-1
uci - 2018-03-24-5d2bf09e-1
uclient-fetch - 2017-11-02-4b87d831-1
uqmi - 2016-12-19-8ceeab69-3
usb-modeswitch - 2017-12-19-f40f84c2-1
usbutils - 007-8
usign - 2015-07-04-ef641914-1
wireless-regdb - 2017-10-20-4343d359
wpad-mini - 2018-05-21-62566bc2-4
wwan - 2014-07-17-1
zlib - 1.2.11-2
[Multiple cdc-wdm devices on Sierra Wireless QMI modems enables] concurrent connections to more than one APN before the qmap muxing feature was added.
https://lists.freedesktop.org/archives/libqmi-devel/2017-June/002373.html
Sierra Wireless MC7455|EM7455 AT Command Guide mirror
You can update your firmware with OpenWRT if you install libqmi. It's buildable from modemmanager-openwrt. It might be smart to just use modemmanager, but it's not required.
https://sigquit.wordpress.com/2016/12/09/qmi-firmware-update-with-libqmi/
# Match these values with the firmware image
qmicli -d /dev/cdc-wdm0 --dms-set-firmware-preference="05.05.63.01,005.037_000,SPRINT"
qmicli -d /dev/cdc-wdm0 --dms-set-operating-mode=offline
qmicli -d /dev/cdc-wdm0 --dms-set-operating-mode=reset
# Wait for a single /dev/ttyUSB device to appear.
# Add --ignore-mm-runtime-check id modem manager isn't installed
qmi-firmware-update -t /dev/ttyUSB0 --update-qdl SWI9X15C_05.05.63.01.cwe SWI9X15C_05.05.63.01_S_005.037_000.nvu