Unfortunately, I have still not gotten my phone dialer set up. I discovered, however, that there must be a very basic problem.
I went to a Command Prompt and typed:
Echo ATDT >Com3
which - from everything I've read here in the forum, in the communication link Bob Hansen was kind enough to provide and elsewhere - SHOULD work and I should HEAR a dial tone. I do NOT hear a dial tone.
Alternatively I added the colon, as suggested and typed:
Echo ATDT >Com3:
and that did not work. (I also tried tried it including %1 and with an actual phone number and that made no difference).
I know that the echo command works because when I typed:
Echo Hello World
I saw Hello World on the screen.
I know that the piping works because when I typed:
Echo Hello World > LPT1
Hello World printed on my HP Laserjet 5 printer.
I know that the modem itself works because when I use MS Access' built-in phone dialer (WOULDN'T IT BE NICE TO HAVE ONE IN SESAME!!! - hint hint)

the dial-tone works just fine and my call is properly executed.
So, now, I am waiting until I can discuss this with my 'hardware/Windows XP' expert to see whether he has any suggestions.
Walk-To-Fly - I appreciate your suggestion about the Q&A 5.0 phone dialer file; however, I would prefer not having to convert a database from Q&A (which I haven't done yet) and I don't necessarily need the other features (such as reminders which I can handle within Sesame). Also, I prefer to get the batch file working because then I can make my own choices such as whether I want to provide a command button for each phone number (home, work, etc.) or whether I can handle it by on-focus of the layout element, or a list, etc. etc. I will certainly keep this software in mind, though and thank you for recommending it.
It is just very frustrating that I was able to do this so easily with Q&A 5.0 as long as nine years ago and am having so much difficulty getting it to work in Sesame (and/or Windows XP).
Finally, in case anyone is interested, when I typed
mode com3: baud=9600 parity=n data=8 stop=1
this was my on-screen result:
C:\>mode com3: baud=9600 parity=n data=8 stop=1
Status for device COM3:
Baud 9600
Parity: None
Data Bits: 8
Stop Bits: 1
Timeout: ON
XON/XOFF: OFF
CTS handshaking: OFF
DSR handshaking: OFF
DSR sensitivity: OFF
DTR circuit: ON
RTS circuit: ON
(whatever that means)