Send SMS with a GSM or 3G Modem

Wavecom GSM modem

Wavecom Fastrack Supreme GSM modem

GSM Modems

A GSM modem or SIM box is basically a GSM phone without keyboard, speaker, battery and display. The terms SIM box, GSM gateway or GSM router are mostly used for devices that route phone calls through the GSM network and the term GSM modem for devices specialized in wireless data transmission. However for GSM modem software they often are interchangeable.

Diafaan SMS Server can use GSM modems and SIM boxes confirming to the ETSI TS 100 585, GSM 07.05/07.07 standard. This includes a broad range of devices like the WaveCom Fastrack, Siemens, Nokia, Huawei or Option GSM modems and a large number of normal GSM phones.

A GSM modem provides the SMS software with a secure gateway to the GSM network, with only two limitations. The amount of SMS message that can be sent and received is limited to approx. 12 messages per minute and it is not possible to send SMS messages with alternative numeric or alphanumeric sender id's.

GSM modem software

GSM modem software always uses a serial port to connect to the GSM modem. This does not have to be a real serial port, virtual serial ports can be used if the server does not have any physical serial ports. This way USB ports and bluetooth connections can also be used by the software. Some GSM modems, like the Huawei E220, or the Wavecom GO are connected directly to the USB port.

Siemens tc35i GSM modem

Siemens tc35i GSM modem

GSM modem on the serial port

GSM modems are connected to your server or workstation with a serial port or USB connection. Connecting your GSM modem with a serial cable is a very secure way to use a GSM modem. No extra drivers are necessary and the cable can be fixed tightly to the server and the GSM modem. GSM modems are optimized for SMS and data transmission and often support advanced options like automatic resets and on-board software.

GSM modem on the USB port

Recent GSM modem models are usually equipped with a USB port. If you have a model with a serial port and you do not have a free serial port available, your GSM modem can be connected to the server with a USB to RS-232 serial port converter. The only difference with a direct serial port connection is that an extra software driver is necessary. The driver installs a virtual serial port that is then used by the Diafaan SMS Server.

Huawei E220 USB GSM modem

Huawei E220 USB GSM modem

GSM phones

Most GSM phones support the GSM 07.05 standard and can be used as a GSM modem. For non-supervised systems, a dedicated GSM modem is a more secure option but for less critical applications a GSM phone is a very cost-effective way to send and receive short messages. A GSM phone can be connected to the server in a number of ways. On older phones a serial port connection is often available, newer phones usually support a USB connection or bluetooth.


Most smartphones can be used with short message software to send messages but often not to receive messages. The reason is that older phones store the received SMS messages on your phone's SIM card, the short message software reads the message list from the SIM card and then removes them to make room for new messages. Many smartphones like the Nokia Symbian phones store the messages in the internal memory of the phone and cannot be read out by the SMS software.

See also: Prepare the SIM card