What is a GSM Modem?
A GSM modem is a device that behaves like an ordinary telephone modem. The difference is that a telephone modem sends data through a phone line while a GSM modem sends data through radio wave. A GSM modem can accept the extended AT commands defined in the GSM standard. With the extended AT commands, you can do things like sending SMS messages, checking the delivery status, etc, from your PC. Besides, you can use a GSM modem to connect to the Internet just like an ordinary telephone modem. For example, a laptop user can connect to the Internet through a GSM modem, say, on a bus.
A GSM modem can be an external device or a PC Card installed on a laptop.
Which is Better: Mobile Phone or GSM Modem?
In general, a GSM modem is recommended for SMS applications. This is because some mobile phones have certain limitations. For example, you may not be able to use some mobile phone models to receive concatenated SMS correctly. A concatenated SMS is a message that can contain more than 160 characters (A normal SMS can contain at most 160 characters). A concatenated SMS is sent as multiple SMS messages. When these SMS messages reach the destination, the mobile phone will try to combine them back to one message.
In addition, you may not be able to receive MMS correctly with some mobile phone models, since they handle the MMS message automatically instead of forwarding the MMS to the PC.
Besides the above issues, mobile phones and GSM modems are more or less the same. Actually, you can consider an AT command enabled mobile phone as “GSM modem + keypad + display”.
There is not much difference between the two in terms of transmission rate, since the determining factor for the SMS sending rate is the wireless network.
Novice developers can use their mobile phones to do some tests, since this will not cost extra money if you already have a mobile phone. A GSM modem will be a better choice in the long term. As you know, manufacturers do not expect you to switch on the mobile phone all the time, nor do they expect you to charge it by the adapter 24-hour a day.
Which GSM Modem Should I Buy?
That depends very much on your budget. You should choose a GSM modem that comes with detail and well-written guides and manuals. This is very important to a developer. Good guides and manuals can always save you a lot of time during development.
You should visit the manufacturers’ website to find a GSM modem that suit your application most. Some GSM modem manufacturers are listed below for your reference (in alphabetical order).
Nokia
Example models: Nokia 12, Nokia 30, Nokia D211 (PC Card).
Siemens
Example models: Wireless module TC45, TC35i, MC35i.
Sierra Wireless
Example models: the Aircard series (PC Card).
Sony Ericsson
Example models: GR48, GM48.
Wavecom
Example models: Fastrack M1306B, Integra M2106.
Original Source : http://www.developershome.com/sms/GSMModemIntro.asp