OK, in my haste I left out the "why" part of my previous post.
 
We had a similar problem where we were unable to make a connection.  The
modems would negotiate, the indicator lights would look good, and then
the carrier would drop.
 
We connected a protocol analyzer between the modem and system and found
that the modem was sending a "RING" message to the HP.  The HP apparently
tried to speed sense using the "RING" message (which just so happened to
begin with a <CR>).  The speed sense was OK (correct rate), and the HP
sent back its prompt.  The modem ignored the prompt (fortunately) as it
was busy negotiating the connection.  When the negotiations were
complete, it sent a series of lines somewhat like:
 
   CARRIER 9600
 
   PROTOCOL LAP
 
   CONNECT 19200
 
There were <CR> characters at the end of each line, and the HP 3000
dutifully treated each line as a logon attempt.  Three invalid logon
attempts and it dropped the connection.
 
Changing the modem configuration so that it would not send the "RING",
"CARRIER", "PROTOCOL", and "CONNECT" messages solved the connect problem.
 
John