The data access arrangement (DAA) is the means by which a modem's circuitry interfaces with the higher-voltage telephone lines. It is also known as a telephone line interface circuit or module, and can also be found in such things as fax machines and other telephone-connected electronic equipment.
Unfortunately, most DAAs are designed for the stantard public telephone network and that network only. When hooked up to higher-voltage private networks, such as those found in hotels, businesses, schools and colleges, the DAA will blow a fuse (if you're lucky) or fry the DAA itself, rendering the modem useless. Trust me. This just happened to me. That's why I'm writing this node.
Some DAAs will accept the higher voltages associated with private networks, but better safe than sorry: you can purchase voltage attenuators for telephone jacks if you want to use your modem one of these two places.
Some of this info was taken from byte.com and whatis.com.