RAM is a mobile data network utilizing the Mobitex Communications system. It's a cellular and packet-based network operating at the 800mHz range, and frequently used in the operation 2-way pagers and vehicle dispatch systems.
It has the upside of being a very simple to use system, and has a very acceptable range due to the radio requencies used. The Mobitex system employs is also an open design allowing for easier adoption. Coverage is available in most US Metropolitan areas.
The drawbacks are its low data transmission speed, usually maxing out at 8Kbps, and difficulties in working on a 'true' IP level; most RAM traffic must pass thorugh a proxy before it can got the the mobile device in question (Though this is a problem with the service networks themselves, not the system as a whole).
Several devices use this network, the most well known being the RIM 950 and 957 2-way communcators and the USR Allpoints Wireless Modem.
Primary competitors to RAM include ARDIS and CDPD.