Sign up for a Nexmo account for your API Key and API Secret if you don't already have one.
You'll need to add YOUR_API_KEY & YOUR_API_SECRET to nexmo.rb and you email address & password to app.rb.
If you're following along with the tutorial out check out the start-here branch
$ git clone git@github.com:ChrisGuzman/sinatra-caller-id.git
$ cd sinatra-caller-id/
$ gem install sinatra sinatra-contrib pony
$ ruby app.rb