NetworkManager

Add gsm connection:

nmcli c add type gsm ifname <interface> con-name <name> apn <operator_apn> username <user> password <password> pin <PIN>

connection configurations

docs

lte

Add your apn and the sim pin if the card is locked lte.nmconnection

[connection]
id=lte
uuid=e555c097-f331-4fab-95a7-8fdf0ebdbf53
type=gsm
autoconnect=false

[gsm]
apn=your_apn_here

[ipv4]
method=auto

[ipv6]
addr-gen-mode=default
method=auto

[proxy]

yocto

cellular modems

Enable qmi & mbim support in kernel using this configuration fragment:

CONFIG_USB_NET_CDC_MBIM=m
CONFIG_USB_NET_QMI_WWAN=m
CONFIG_USB_WDM=m

Create an networkmanager_%.bbappend:

FILESEXTRAPATHS:prepend := "${THISDIR}/${PN}:"

SRC_URI += "file://lte.nmconnection"

PACKAGECONFIG:append = " modemmanager "

do_install:append() {
    install -m 0600 ${WORKDIR}/lte.nmconnection ${D}${sysconfdir}/NetworkManager/system-connections/lte.nmconnection
}