If you have a Notebook with an embedded WWAN device (GSM/LTE/5G) and want to quickly send a SMS message, there is a way to do this with mmcli (ModemManager CLI):
1st: List the available modem devices:
$ mmcli list
2nd: Sent the SMS via an available modem (in my case moden no. 0):
$ mmcli -m 0 --messaging-create-sms="text='Hello world',number='+1XXXXXXXXXX"
Messaging | created sms: /org/freedesktop/ModemManager1/SMS/7
3rd: Use the ID of the message and send it to the ether:
$ mmcli -m 0 --sms 7 --send
successfully sent the SMS
That's it. You can also read incoming SMS with mmcli by listing them with "mmcli -m 0 --messaging-list-sms" and then reading the invidual messages by their ID with "mmcli -m 0 --sms ID --send"