Want to find a device I can plug in between my phone and the wall that
will allow me control of the outgoing call volume. I want to use my
existing phone. I do not want a new phone (i.e. Walker brand phones
for hearing impared).

I'm glad to have been able to assist you in finding what you need. I
have reposted the link below.

Your Factory Source: Vista M12 Amplifier
http://store.yahoo.com/your-factory-source/viam.html

Using a Froogle search, I found a much better price for the device:

Axion Tech: PLANTRONICS M12 Amplifier Vista Universal Amplifier 
http://www.axiontech.com/prdt.php?src=FG&item=32078

Froogle search strategy:

Froogle Search: telephone amplifier outgoing volume
://www.google.com/froogle?hl=en&tab=wf&q=telephone+amplifier+outgoing+volume&scoring=p

Hope this helps you to crank up the volume!

Best regards,
pinkfreud

Timely and helpful information.

This might do the trick:

http://www.wholesalers-direct.com/a20b.html

Another possibility:

http://store.yahoo.com/your-factory-source/viam.html

There are some problems. Your phone company does not want you to have
such a device, as it would be capable of putting excessive signal on
the phone cable causing cross talk to other phone lines. Your phone
company has such a device, but tight specs and extra features make
them expensive. It may be practical to modify a cheap obsolete
computer modem for your purposes, but I don't have the know how.  
Neil

Hi

Pinkfreud you answered my question with the second link. Thank you!
Please post as an answer so I can pay you.