I normally want the cellular modem disconnected unless it receives data over ethernet 0. It then passes through that data by dialing, send the data, and then disconnects again. The mdoem of course also answers incomming calls, and then passes the data sent to it to ethernet 0. The probelm I have now is that the modem is always connected, I do not want that.
It is easy enough to set an RX or TX timeout to disconnect the cellular and stop it auto dialling but only dial when traffic is needed.
“ppp 1 timeout x” and “ppp 1 rxtimeout x” where x is in seconds to wait before it disconnects.
and to stop autodial it is “ppp 1 aodion 0”
I would also suggest firewalling the ethernet to only allow your interesting traffic. Many computers create a lot of different traffic that could request the connection to come up.
But I think you might not understand how this all works if you want the modem to answer incoming calls. You cannot call these devices. They are data only. If you disconnect the cellular service you are essentially “unplugging the cable” so I am not sure how you imagine it would work from a remote location to request the data connection to come up.
The only real option would be to SMS the device first to request the connection to come up (if your device supports SMS).