Where can I get a copy of an owner's manual (hard copy or downloadable
or online) for a GE Proseries 3line telephone?  It appears that GE is
the brand (logo on the front) and Thomson Consumer Electronics is the
manufacturer (from the serial number label on the back.  There are
many numbers on the back, but it appears that this model is number
2-9439B HAC.

In 1988 Thomson Consumer Electronics purchased the rights to the names
GE and RCA, and subsequently manufactured a number of items under
those labels, including your particular telephone.  In 1995, the
company changed its name to Thomson Multimedia, by which name it is
still known now.
 
The main company website is at: http://www.thomson-multimedia.com/ . 
Their headquarters is located at:
Thomson multimedia Inc.  (Headquarters)  
10330 North Meridian Street  
INDIANAPOLIS - IN 46290 - 1976  
TEL : (1 317) 587 3000  
FAX : (1 317) 587 6765  
 
A call to the main number got a CSR who gave me the number for their
GE products department at (580) 634-0135.  The operator at that number
directed me to either the RCS website at http://www.rca.com or to
(800) 338-0376 (the GE/RCA Parts & Accessories Dept.) to order a hard
copy.  I could not locate your product by model number on the website.
 The person I spoke with at the “800” number said that the owners
manual for your model is not available in hard copy.  Furthermore,
downloadable manuals are not archived for any models older than ten
years, and in the case of telephones, would not be available for
models more than “a couple of years” old.  She gave me the phone
number for the technical help/troubleshooting department at (800)
336-1900 and said they could help if you were having a problem - even
with older models.
 
I know this isn’t what exactly what you were hoping to find, so I’ve
posted it as a comment.  However, if it’s satisfactory to you, please
let me know and I’ll post it as an answer.
 
Best wishes, 
Byrd

Very helpful.  Byrd pointed me in the right direction, I made an
additional call and got what I needed.  Very good!

In 1988 Thomson Consumer Electronics purchased the rights to the names
GE and RCA, and subsequently manufactured a number of items under
those labels, including your particular telephone.  In 1995, the
company changed its name to Thomson Multimedia, by which name it is
still known now.

The main company website is at: http://www.thomson-multimedia.com/ . 
Their headquarters is located at:
Thomson multimedia Inc.  (Headquarters) 
10330 North Meridian Street 
INDIANAPOLIS - IN 46290 - 1976 
TEL : (1 317) 587 3000 
FAX : (1 317) 587 6765 

A call to the main number got a CSR who gave me the number for their
GE products department at (580) 634-0135.  The operator at that number
directed me to either the RCS website at http://www.rca.com or to
(800) 338-0376 (the GE/RCA Parts & Accessories Dept.) to order a hard
copy.  I could not locate your product by model number on the website.
 The person I spoke with at the “800” number said that the owners
manual for your model is not available in hard copy.  Furthermore,
downloadable manuals are not archived for any models older than ten
years, and in the case of telephones, would not be available for
models more than “a couple of years” old.  She gave me the phone
number for the technical help/troubleshooting department at (800)
336-1900 and said they could help if you were having a problem - even
with older models.

I know this isn’t what exactly what you were hoping to find, so I’ve
posted it as a comment.  However, if it’s satisfactory to you, please
let me know and I’ll post it as an answer.

Best wishes,
Byrd

I called the 800 number you recommended and they sent me to a website,
www.thomsonservice.com and walked me through how to order an owner's
manual.  I am about to buy one for $8.50.

I would not have found this without Byrd's help, so please submit as
an answer.  Once your answer is posted, I will close this question.  I
will not accept any other answers.

THANK YOU!

Thank you, tks!  I'm really glad you found your manual! 

-- Byrd

THIS QUESTION HAS BEEN ANSWERED AND IS NOW CLOSED.