 
White Paper: Cellular Direct Connect 
 
AT&T Paradyne 
8545 126th Ave N. 
Largo, Fl   34635 
800-482-3333 (or 813-530-8623) 
 
 
 
 
How do I connect a modem to a cellular phone? 
============================================= 
There are two primary ways of  connecting a modem to a cellular phone: 
1. RJ11 Adapter Box 
2. Direct Connect Cable 
 
Each of these is described below. 
 
1. RJ11 Adapter Box 
Modems are designed to interface to the PSTN (Public Switched  
Telephone Network -- the "dial" network.)  As such, they require call  
progress and signaling information from the telephone company Central  
Office (CO).  Examples of these signals are: off-hook indication to the  
CO, dial tone from the CO, touch tones to the CO, etc. 
 
Cellular phones do not provide this signaling information required by  
the modem.  They provide their own proprietary interface, which has  
been designed for cellular phone accessories (hands-free kits, etc.)   
 
A special adapter box  can be placed between the modem and the  
phone.  This box is called an "RJ11 Adapter Box".  (The name comes  
from the "RJ11" connector that the modem plugs into for PSTN  
operation.)  This RJ11 Adapter Box provides the necessary conversion  
between the signals required by the modem and the signals required by  
the cellular phone.   
 
2. Direct Connect Cable 
RJ11 Adapter Boxes are necessary because regular dial modems were  
never meant to be connected to cellular phones.  Conversely, a modem  
with Direct Connect is designed from the start to interface to the  
cellular phone -- all the necessary mechanical, electrical, and software  
"hooks" are included in the modem.  Thus, the interface between the  
modem and the phone is nothing more than a simple cable (the "Direct  
Connect Cable"). 
 
Since users will also want to connect to the PSTN, Direct Connect  
modems usually have two connectors:  
1. A PSTN connector for the dial network 
2. A Direct Connect connector for interfacing to the cellular phone 
 
 
 
What are the advantages of Direct Connect? 
========================================== 
Direct Connect offers numerous advantages over RJ11 Adapters: 
 
1. Less Clutter 
A Direct Connect Cable is much less cumbersome than the extra box and  
cables required for RJ11 Adapter Boxes.  When you are mobile, the less  
equipment you have to carry the better. 
 
2. Less Cost 
RJ11 Adapter Boxes usually cost over $300.  This is typically more than  
the price of the modem or the phone!  Direct Connect Cables for AT&T  
Paradyne modems are usually priced around $50 (slightly more for certain  
phones). 
 
3. No batteries 
RJ11 Adapter Boxes require a battery.  (RJ11 Adapter Boxes for 3-W  
phones usually are powered from the phone.)  This battery usually has a  
short life -- and is prone to fail at the worst time!  A Direct Connect Cable  
requires no batteries. 
 
4. Better Performance 
Direct Connect offers a "cleaner" audio interface to the phone -- higher  
speeds and greater connection reliability is obtained. 
 
 
 
Where do I connect to the phone? 
================================ 
Handheld phones usually have a connector on the bottom of the phone.   
Three watt phones (mobile and transportable) require a "T" connector that  
allows the handset and modem to plug together into the transceiver. 
 
 
 
What about PCMCIA vs. Pocket Modems? 
==================================== 
AT&T Paradyne offers Direct Connect with its KeepInTouch PCMCIA  
modem.  A PCMCIA modem coupled with a Direct Connect Cable is the  
best alternative for mobility.  Compare this to a Pocket Modem with an  
RJ11 Adapter Box: 
 
1. Clutter 
PCMCIA Modem + Direct Connect Cable 
vs.  
Pocket Modem + RS232 cable + Pocket Modem charger + RJ11 Adapter Box  
+ RJ11 Adapter Box Charger + Extra cables between the pieces 
 
2. Batteries 
Try maintaining four devices with batteries -- the Computer, the Cellular  
Phone, the RJ11 Adapter Box, and the Pocket Modem -- long enough to  
make a cellular call!   
 
 
What phones are supported by AT&T Paradyne? 
=========================================== 
While several other modem manufacturers support a limited number of  
phones, the AT&T Paradyne KeepInTouch card supports the widest  
variety of phones in the industry. 
  
The following is the current list of phones supported by the KeepInTouch  
card. This list is constantly being updated as new phones are added -- call  
AT&T Paradyne at 800-482-3333 for the latest list. 
 
AT&T                   3610, 3710, 3730, 3760, 3830, 3850, 6650 
Nokia                  121, PT128, 232, 2120 
Technophone            415, 515, 815 
NEC                    P110, P120, P180, "TalkTime" series 
 
Many phones are "private labeled" with the name of the Cellular Service  
Provider.  If you have a phone labeled as such, contact your Cellular  
Service Provider to see if your phone is on this list.  
 
 
 
 
