~$ gsmsendsms -h gsmsendsms: [-b baudrate][-c concatenatedID][-C sca][-d device][-h][-I init string] [-t][-v][-X] phonenumber [text]

  -b, --baudrate    baudrate to use for device (default: 38400)
  -c, --concatenate ID for concatenated SMS messages
  -C, --sca         SMS service centre address
  -d, --device      sets the destination device to connect to
  -h, --help        prints this message
  -I, --init        device AT init sequence
  -r, --requeststat request SMS status report
  -t, --test        convert text to GSM alphabet and vice
                    versa, no SMS message is sent
  -v, --version     prints version and exits
  -X, --xonxoff     switch on software handshake

  phonenumber       recipient's phone number
  text              optional text of the SMS message
                    if omitted: read from stdin

(it's in the gsm-utils package)

I'm curious what you'd consider a GSM or SIM firewall to look like. Typically from the perspective of Linux, a "old and busted" telephony devices will appear as a TTY which a (relatively) privileged process can use as a control channel and/or to set up a PPP interface. On devices supporting "the new hotness", you get a special character device that speaks the MBIM or QMI protocols for a control channel, and an "ethernet" interface for IP traffic.

In both cases, access to the SIM is limited to processes that can speak to the telephony device's control channel, and the data side is firewalled with iptables like any other network interface. To further restrict access to telephony device capabilities you can break out ModemManager or oFono along with Polkit.

Things get a little wonky when you start to talk about voice calls, as there isn't a lot of standardization in how to get the audio channel in/out of linux on telephony devices yet, but ofono and telepathy seem to have made strides in that direction.

Oh, I do agree. The problem is - who's going to write it? I'm an one-man army so far, this is going to change once people get their hardware from the first batch I'm finishing now, but for now the project still needs contributors.