If you are trying to process SMS messages manually you need to ensure that the SMS polling interval is set to zero and the SMS caller ID is removed. Otherwise, the router will try and process the messages.
CLI commands are:
modemcc 0 sms_interval 0
modemcc 0 sms_callerid !
then do 'readsms'
then do 'showsms'
readsms will take the SMS from the SIM into a memory buffer
showsms should display the SMS on-screen in the terminal emulator.
Mar 20, 2019