A GSM modem is a specialized type of modem which accepts a SIM card, and operates over a subscription to a mobile operator, just like a mobile phone. From the mobile operator perspective, a GSM modem looks just like a mobile phone.

For the purpose of this document, the term GSM modem is used as a generic term to refer to any modem that supports one or more of the protocols in the GSM evolutionary family, including the 2.5G technologies GPRS and EDGE, as well as the 3G technologies WCDMA, UMTS, HSDPA and HSUPA.

A GSM modem exposes an interface that allows applications such as NowSMS to send and receive messages over the modem interface. The mobile operator charges for this message sending and receiving as if it was performed directly on a mobile phone. To perform these tasks, a GSM modem must support an "extended AT command set" for sending/receiving SMS messages, as defined in the ETSI GSM 07.05 and and 3GPP TS 27.005 specifications.

GSM modems can be a quick and efficient way to get started with SMS, because a special subscription to an SMS service provider is not required. The mobile operator charges for this message sending and receiving as if it was performed directly on a mobile phone. In most parts of the world, GSM modems are a cost effective solution for receiving SMS messages, because the sender is paying for the message delivery.

A GSM modem can be a dedicated modem device with a serial, USB or Bluetooth connection.

Historically, we have recommended GSM modems from manufacturers such as Multitech, Falcom, Siemens (now Cinterion), iTegno and Wavecom. While these manufacturers make very good GSM modems, there are currently a lot of GSM/3G USB stick modems available on the market, which are less expensive (under $100), and in many cases significantly faster than older GSM modems.

Some recommended GSM/3G USB modems include the Option ICON 322, Sierra Wireless Compass 885, SonyEricsson MD300, Novatel MC950D and Huawei E160. Many other models from these manufacturers will also work well with NowSMS.

We have posted some notes about experiences with specific modem models at the following link: http://blog.nowsms.com/search/label/GSM%20modem

A GSM modem could also be a standard GSM mobile phone with the appropriate cable and software driver to connect to a serial port or USB port on your computer. Any phone that supports the "extended AT command set" for sending/receiving SMS messages, as defined in ETSI GSM 07.05 and/or 3GPP TS 27.005, can be supported by the Now SMS/MMS Gateway. Note that not all mobile phones support this modem interface.

Due to some compatibility issues that can exist with mobile phones, using a dedicated GSM modem is usually preferable to a GSM mobile phone. This is more of an issue with MMS messaging, where if you wish to be able to receive inbound MMS messages with the gateway, the modem interface on most GSM phones will only allow you to send MMS messages. This is because the mobile phone automatically processes received MMS message notifications without forwarding them via the modem interface.

It should also be noted that not all phones support the modem interface for sending and receiving SMS messages. In particular, most smart phones, including Blackberries, iPhone, and Windows Mobile devices, do not support this modem interface at all.

Nokia phones that use the S60 (Series 60) interface, which is Symbian based, only support sending SMS messages via the modem interface, and do not support receiving SMS via the modem interface. Nokia phones using the Series 40 3rd Generation or later interface have similar limitations and do not support receiving SMS via the modem interface. This makes most Nokia phones incompatible with the 2-way SMS functionality of NowSMS.

SonyEricsson phones generally have a good full GSM modem implementation (except for the P and X series which use UIQ/Symbian or Windows Mobile). They can be used for sending/receiving SMS messages and sending MMS messages.

Motorola phones have a bug in their GSM modem implementation that prevents them from being able to send binary SMS messages. They can send/receive SMS text messages, and send MMS messages.

While using a phone as a modem may be a good way to get started with NowSMS, the best solution is to use a dedicated GSM modem device, such as the GSM/3G USB modems mentioned earlier on this page.

Additional notes about experiences with specific modem models can be found at the following link: http://blog.nowsms.com/search/label/GSM%20modem