This short tutorial illustrates how to create a tropo messaging (sms/im) application, using its web APIs, with the same code base, in about 15 minutes.

First you need to install tropo's ruby gem, which makes parsing so much simpler.
sudo gem install tropo-webapi-ruby

Also check out github for its documentation and examples (sinatra)
http://github.com/voxeo/tropo-webapi-ruby

Create a rails application
(note that there is an incompatibility issue with ActiveSupport 2.3.2 and json, which is requied by tropo ruby gem.  I'm using rails 2.3.5 and it works fine.)

rails tropo-tutorial
cd tropo-tutorial
script/generate controller messagings # we will use this controller to essentially parse tropo request and response appropriately

# somple content of messagings_controller.rb
class MessagingsController < ApplicationController
  def index
    #initial_text captures the very first sms or IM sent to tropo
    initial_text = params["session"]["initialText"]
    from = params["session"]["from"]
    network = from["network"]
    from_id = from["id"] # this field contains IM login or phone number in case of incoming SMS
    if network == "SMS" || network == "JABBER"
      render :json => parse(initial_text)
    else
      render :json => Tropo::Generator.say("Unsupported operation")
    end
  end

  private

  def parse(input)
    input.strip!
    # do whatever parsing you need.  in this example, if user types "n what a new day", tropo will
    # respond him with "you said: what a new day"
    if m = input.match(/^(n|N)\s+/)
      Tropo::Generator.say "you said: " + m.post_match
    else
      Tropo::Generator.say "Unsupported operation."
    end
  end
end

Here is an example of what Tropo posts to our messagings_controller.
Processing MessagingsController#index (for 127.0.0.1 at 2010-02-09 16:19:29) [POST]
  Parameters: {"session"=>{"timestamp"=>"2010-02-10T00:19:01.718Z", "from"=>{"name"=>"unknown", "network"=>"SMS", "id"=>"14085059096", "channel"=>"TEXT"}, "to"=>{"name"=>"unknown", "network"=>"SMS", "id"=>"16175759989", "channel"=>"TEXT"}, "userType"=>"HUMAN", "id"=>"p8rzeh", "initialText"=>"Zzzzz", "headers"=>[{"value"=>"70", "key"=>"Max-Forwards"}, {"value"=>"124", "key"=>"Content-Length"}, {"value"=>"<sip:10.6.93.201:5066;transport=udp>", "key"=>"Contact"}, {"value"=>"<sip:9991444206@10.6.93.202:5061;to=16175759989>", "key"=>"To"}, {"value"=>"1 INVITE", "key"=>"CSeq"}, {"value"=>"SIP/2.0/UDP 10.6.93.201:5066;branch=z9hG4bK7oo7k1", "key"=>"Via"}, {"value"=>"p8rzeh", "key"=>"Call-ID"}, {"value"=>"application/sdp", "key"=>"Content-Type"}, {"value"=>"<sip:370930B3-D767-4F35-9A9AABB4535A61AB@10.6.61.201;channel=private;user=14085059096;msg=Zzzzz;network=SMS;step=2>;tag=mbx865", "key"=>"From"}], "accountId"=>"38958"}, "tropo-engine"=>"json"}

Add a route for the messageings_controller in config/routes.rb
map.connect 'messaging', :controller => 'messagings', :action => 'index'
Note that I'm calling the route messaging, without the 's'; and I'm calling the controllers messages_controller, with the 's'.

Add a gem require in config/environment.rb
require 'tropo-webapi-ruby'

Now it's time to create a tropo app and activate an IM/SMS account.  
I like to use @bot.im's jabber account.  For this example, I have created foobuz@bot.im.
Once your tropo IM account is activated, go ahead and add it to your IM client (a jabber client in this exmaple)
Next you need to supply a url that powers voice calls as it is required by Tropo.  Just put in any url for now as we won't deal with voice here, for now.

Then supply a url that powers SMS/messaging calls.  Since we deal with Tropo web api (v.s. hosted script), we will need to supply a valid server url that points to a rails controller for example.
http://tropo-tutorial.heroku.com/messaging?tropo-engine=json

please note that "tropo-engine" is a required parameter for Tropo.  The value for it is json in this example.

Now add a sms-enabled number.

That's it, now fire up your rails server.  For this example, I have created a working Heroku app for you test with.  You can add foobuz@bot.im and/or SMS to (617) 575-9989,
If you send message: "this is a test"
Tropo should respond "unsupported operation"
If you send message: "n this is a test"
Tropo should respond "you said: this is a test"

Now for the bonus point, let's give tunnlr a swirl.

tunnlr is great for developing sms/im apps locally without having to deploy your application on to a server.  You can sign up for tunnlr http://tunnlr.com.  Now you can take a look at the github source code for tunnel.yml under the config directory.  Fill in the field according to the credential tunnlr.com gives you.

Start your rails server, then issue: rake tunnel:tunnel:start
This should start a reverse ssh tunnel for you and redirect all the http traffic through the tunnel to your local machine.  If you decide to use tunnlr, you would need to change your tropo app's configuration and point the url to your tunnlr url.  It should look like http://your_tunnlr_host.com:port

send message to your IM bot (created on tropo) or SMS to the tropo number.
e.g. "this is a test"
tropo should respond "unsupported operation"
e.g. "n this is a test"
tropo should respond "you said: this is a test"

An example of the conference API:
http://docs.tropo.com/webapi/2.0/frame.jsp?page=conference.htm

I added a new rails controller for this:
script/generate conferences

Add this to routes.rb (I will just use index action)
map.connect 'conference', :controller => 'conferences', :action => 'index'

Now open conferences_controller and add index method:
  def index
    render :json => Tropo::Generator.conference(
                    :name => "foo",
                    :id => "1234",
#                   :exitTone => "#",
                    :on => [
                                {
                                        :event => "join",
					:say => { :value => "Welcome to my conference" }
                                },
                                {
                                        :event => "leave",
                                        :say => { :value => "Someone has left the conference" }
				}
                           ])
  end
A few things to note for the code above:
You really just need :id and :name (maybe not even both of them) to have a conference call.  
The :on works for the join event where I can hear "Welcome to my conference", but sometimes I can't hear the first word "Welcome".  It maybe beause system is trying to establish SIP session.
I haven't gotten the leave event working and couldn't hear "Someone has left the conference".
Also the second caller joining the conference hears the word "conference" in the welcome message being echoed several times.  The conference call itself works well, pretty clear voice quality when I tested with a coworker.