I realize this is an old thread but I found it when trying to get an QUECTEL EC-25 modem working. I am running the Raspian OS image provided by Balena and a SIM from Hologram on the T-mobile (USA) network. I was able to get this working quite easily using the software packages provided by Sixfab: QMI Interface Internet Connection Setup Using Sixfab Shield/HAT
I had used their LTE HAT on another project and it works out that their scripts worked well setting up the qmi interface on the Quectel modem installed in the balena-fin.
Only one thing is not documented. You must put ‘denyinterfaces wwan0’ as the first line in your /etc/dhcpcd.conf file.
$ lsusb
Bus 001 Device 006: ID 413c:2107 Dell Computer Corp.
Bus 001 Device 005: ID 2c7c:0125 Quectel Wireless Solutions Co., Ltd. EC25 LTE modem
Bus 001 Device 003: ID 0424:ec00 Standard Microsystems Corp. SMSC9512/9514 Fast Ethernet Adapter
Bus 001 Device 002: ID 0424:9514 Standard Microsystems Corp. SMC9514 Hub
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
dmesg | grep ttyUSB
[ 6.367215] usb 1-1.2: GSM modem (1-port) converter now attached to ttyUSB0
[ 6.372083] usb 1-1.2: GSM modem (1-port) converter now attached to ttyUSB1
[ 6.388624] usb 1-1.2: GSM modem (1-port) converter now attached to ttyUSB2
[ 6.389269] usb 1-1.2: GSM modem (1-port) converter now attached to ttyUSB3
3: wwan0: <BROADCAST,MULTICAST,NOARP,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UNKNOWN group default qlen 1000
link/ether f2:93:7d:2a:f5:7c brd ff:ff:ff:ff:ff:ff
inet x.x.x.x/29 brd x.x.x.x scope global wwan0
valid_lft forever preferred_lft forever
inet6 fe80::f093:7dff:fe2a:f57c/64 scope link
valid_lft forever preferred_lft forever