Every Short Message has to pass the SMSC. There are different ways to tranfer the Short Message to the Short Message Service Centre. A Short message can reach the SMSC by GSM modem / module and can be transferred to an email or fax.
Make a call to a manual reception and tell them what you want to sent and to whom. Not very useful in industrial GSM applications.
Make a call to an automatic answering service and make a choice from a number of ready made texts. Not popular in industrial applications also.
Use your own GSM phone with sending abilities and enter a message and send it. Can be useful, if you have to send control commands from somebody to a machine, to change parameters. Most GSM phone offers the storage of Short Messages so that you can send from memory of the SIM card.
Use a computer with a PSTN modem and a special SMS program. Popular for the sending of Short messages to mobile GSM phones. There are a lot of local SMS programs available. A few of them are freeware and others are shareware. In Germany ( and other countries) the GSM operators offers light versions of SMS programs as freeware. If you have a need for software that have more features, then you have to buy it. If you use a local SMS software, then it is in local language and the parameters are set for your GSM operators. The other technical problem are the different hardware interfaces like PSTN modem or Datex P ( X.25) and the different software protocols like TAP and USP on the SMSC. If you have to send only then TAP is OK, but if you have to send and to receive then UCP is the right way. The UCP can send and receive Short Message. The easiest, but not fastest transmit and receive you can reach with a GSM modem. A GSM modem can send / receive a Short Message each 6 to 10 seconds. With a connect based on UCP you can reach 600 messages per minute.
For industrial applications you can not often not use ready SMS software. You have not to think about the protocols, if you buy software drivers from third parties. That can save time and money.
SMS to fax is available by a lot of GSM operators and by local third parties.
SMS to email is available by the GSM operators and by third parties too.
Email to SMS is available by the GSM providers and by third parties. A few of them offers that serif free of charge, but with advertising on the end of the message. Such free of charge services do mostly not free of charge for commercial GSM solutions.
In the beginning of GSM it was not possible to send an SMS from GSM operator A in Germany to GSM provider B in Germany. A few companies has developed special services to bridge that. They offer sending to “foreign” German operators. Right now they offer a couple off other specials, that are not supported by the local German operators.