Sending a SMS message
Regarding sending SMS from a PLC, there is at least 2 ways to skin the cat:
Useing standard dial-up modem
Check if your national phone provider have a dial-up number to a message center or SMS service center.
The phone number may be differente depending on an analog or ISDN access point.
The procedure is:
- make the modem dial-up the message center, establish connection.
- send data according to a given protocol
- hang-up and the message center will send the message to the GSM phone (or pager)
2 "common" protocol's are: TAP and UCP (Universal Computer Protocol)
Again, check with your provider if there is a message center with dial-up access in your country.
Here in Norway the 2 largest providers both closed their access point (it was free and you could send messages anonymous..), but there is at least one private provider supporting UCP (but not for free...)
Useing a GSM-modem/-terminal
No phone call is started, the message is transmitted to the terminal in command state. Same as sending a SMS message from a GSM phone, appart from that it isn't your fingers that make the message, but serial data from an external equipment, PLC or whatever.
The SMS service center number is not the same as for access via PSTN (Public Switched Telephone Network) or ISDN network. It's the same as you use to send SMS from your mobile phone, that is, if it is the same provider.