sms_sender.rb

community.users.each do |recipient|
  sms_credits = community.sms_credits

  if sms_credits > 0
    send_sms recipient, 'Everything is fine.'

    # take off a credit
    community.sms_credits = sms_credits - 1
    community.save
  end
end

def send_sms(recipient, message)
  # does a REST call to Twilio
  # which takes a while
end