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· Use the right modem Make sure your modem supports one of the leading cellular protocols, which include Enhanced Throughput Cellular (ETC), the Microcom Networking Protocol 10 (MNP10), MNP10-EC (enhanced cellular) and TXCEL. Because a protocol is like a language, it only works if the modems on both sides of the connection speak the same protocol (there's no t ranslation involved). Hence, the fixed-end modem needs to support the same cellular protocol as the mobile modem. Unfortunately, most corporate modem pools, Internet service providers (ISPs) and online service providers do not support these protocols. The solution is to make connections through a modem pool operated by a cellular service provider.

· Use the right phone and cable Although the RJ-11 connector is standard, neither the physical nor the electrical connection to a cellular phone is. Each cellular-capable modem supports only certain makes and models of cellular phones. Check your modem manual. Some low-cost cellular phones don't support data at all.

In addition, you need to use the right direct connect cable, which you usually can obtain from the modem vendor. In general, you will have better success matc hing your modem to your cellular phone with the major brand phones because modem vendors are more likely to support these products.

If you find that your modem does not support your cellular phone, check with your modem vendor to see if it has more recent modem firmware that supports additional phones. If you are using a dual-mode analog/digital cellular phone, you may have to put your phone in analog mode for data calls. How this is done depends on the model of digital cellular phone.

Once you have the matching components, you will experience optimal operation with the phone antenna extended and the phone in a vertical position. For reliable data calls, you want reasonable signal strength and stationary operation.

· Enable cellular protocols For reliable communications, you must enable the modem's cellular protocols. Some modems detect a direct connection to a cellular phone and automatically enable cellular operation. With others (check your modem manual) you need to modify how the m odem is initialized. Most communications applications initialize the modem using a modem initialization string. You may need to add an "AT" command to this string to enable cellular oper ation. This command is different for every modem. Some applications, however, do not provide access to the initialization string, in which case you will need to contact your application vendor for assistance.

Even if your modem can automatically detect the cellular phone, some applications restore the modem to its factory default condition, which can turn off the cellular protocols. In Microsoft Windows95, most modem applications use Microsoft Corp.'s Telephony Application Programming Interface (TAPI), which has a provision to enable cellular operation. Select Modems in the Control Panel and go to Advanced Connection Settings.

· Connect through a modem pool Cellular carriers have installed modem pools at their mobile switching centers that translate between cellular protocols and conventional modem protoc ols. Modem pools consist of pairs of back-to-back modems. When connecting through a modem pool, you create two separate modem links: the link between the mobile and the switch uses cellular protocols while the link between the switch and the fixed-end modem (a corporate remote-access facility, for instance) uses conventional modem protocols (see "Cellular Carrier Modem Pools" diagram below).

To route your call through a modem pool, simply add a prefix of "*3282" (which spells out "data" on your keypad) to the phone number in your application. You need to follow *3282 with a "1" then area code then the number for some data carriers, and just the area code and number for other carriers. A data phone number in Seattle, for example, would have the following format: "*3282-1-206-555-1212." (The modem ignores the hyphens.)