Example of catching Twilio REST exceptions in Ruby - sketch, I don't actually know how this works.

catch.rb

require 'rubygems' # not necessary with ruby 1.9 but included for completeness
require 'twilio-ruby'

# put your own credentials here
account_sid = 'ACxxxxxxxxxxxxxxxxxxxxxxxxxxxxx'
auth_token = 'yyyyyyyyyyyyyyyyyyyyyyyyyyyyyyy'

# set up a client to talk to the Twilio REST API
@client = Twilio::REST::Client.new account_sid, auth_token

begin
    @client.account.sms.messages.create(
      :from => '+14159341234',
      :to => '+16105557069',
      :body => 'Hey there!'
    )
rescue Twilio::REST::RequestError => e
    # do whatever you need to accept the failure gracefully
end