What is a GSM Intercom System?

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GSM stands for Global System for Mobile Communications and is the world's most popular standard for mobile telephony. Here in the U.S. it is used by AT&T and T-Mobile as well as the services that contract to use the networks of these two companies. Other providers in the U.S. such as Verizon and Sprint use a technology called CDMA (Code Division Multiple Access).

Given that GSM is more widely used across the world, and cell phone network intercoms have been popular in other countries such as Europe, at this point only GSM intercoms are available. Manufacturers want to develop equipment that can be used by the widest variety of markets so they can quickly recover development cost and make a larger profit. These intercoms have not been available in the U.S., but are now becoming popular here as well, especially since analog landlines are starting to disappear as confirmed by these statistics:

Telecom industry trade association US Telecom says that traditional wire-line service dropped from 95 percent of U.S. households to 40 percent in 2011.
AT&T wants to get rid of this "dying technology" because the cost of subsidizing remaining customers is becoming prohibitive.
The Technical Advisory Council (TAC) to the FCC recommended that the FCC set a date for the end of the public switched telephone network rather than let the service fade slowly into oblivion as it's now doing.
According to the Centers for Disease Control, as of the second half of 2011, one in three U.S. households (34.0%) had only wireless telephones.
70% of responders to a "Wholesale Voice Buyer Survey" by research firm ATLANTIC-ACM stated that the death of plain old telephone service (POTS) was one of the most disruptive factors impacting responder's businesses.

To use a one of these intercom you simply sign up for a service that uses GSM and you take what's called a SIM (subscriber identification module) card that you get when you sign up, and you place it in a slot inside the intercom control module. When someone presses the button on the intercom, it dials out on the cell phone network and places a call to any landline or mobile telephone, no matter where that phone is. As long as there is cell phone service at the location you want to place the intercom, then you can place it there. You can even power the unit via solar power.

Most of these intercoms can dial multiple telephone numbers until someone answers so visitors at a door or gate are more likely to reach someone. The person reached can press a key on their telephone to activate a switch in the intercom that can be used to open a door or gate remotely. Some GSM intercom enable you to use text messaging to send a message to the intercom to do the same thing.

Another nice feature is their ability to pre-program telephone numbers into the system so certain visitors can just call the intercom, and based on their caller line ID, the door or gate will open. With these intercoms you can: