If a call is "busy", you get immediate feedback in the agent screen (the call TERMINATES with busy as the reason, and the agent is immediately notified).
If a call is "ringing", the called party determines ring tone (if any). In many situations, this results in silence ... which should be interpreted as ringing, as a rule. Alternately, as the previous poster suggested, you can use the loopback dialplan to generate a second call (doubling the workload for the system for the duration of the call) to provide a ring tone from Asterisk to itself for the first leg of the call. On a heavy-use system, this can present a load issue, of course.
Note that neither of these situations will resolve a "35 second wait ... then 'disconnected number'" result. Since that phone company prefers to ignore the call for 35 seconds before responding with the DC message, nothing will fix that scenario except autodial (which would of course fix all of this).
Why are you manual dialing in the first place? I hope these are 3-way calls or "exceptions" and not the main dialing method. If so: You're losing money, LOL
PS: You should include your installation method, with version, in your post with your other specs. If it's not Vicibox or Goautodial ... a link to the installation instructions used is often useful.