Example using SimpleXml to parse API query to LocalCallingGuide.com

local_calling_guide.rb

# lib/local_calling_guide.rb
# This file should be autoloaded when Rails starts

require 'rest_client'
require 'xmlsimple'

class LocalCallingGuide

  def initialize
    @url = "http://www.localcallingguide.com/xmllocalprefix.php"
  end
  
  # This method accepts the first 6 digits of a phone number as two parameters.
  # It will return an array of 6 digit strings which correspond to all local
  #   phone numbers to the number passed in. 
  #
  # For example, given a US number 250.423.2742, npa=250; nxx=423
  def get_numbers(npa, nxx)
    
    # Simple call to the API will yield an XML document, which can be viewed
    # here: http://www.localcallingguide.com/xmllocalprefix.php?npa=250&nxx=423
    api_result = RestClient.get @url, { 'params' => { 'npa' => npa, 'nxx' => nxx, 'dir' => 2 } }
    
    # Extract the lca-data node and its containing array and iterate through all
    # prefix children extracting the npa and nxx for each
    xml_doc = XmlSimple.xml_in(api_result)['lca-data'][0]

    local = []
    
    xml_doc['prefix'].each { |obj|
      local.push obj['npa'][0] + obj['nxx'][0]
    }

    local
  end

end

your_controller.rb

# Assuming you have been passed a parameter :number
number = params[:number]

# Use your class
lcg = LocalCallingGuide.new.get_numbers(number[0..2], number[3..5]).to_json

# Yields:
#    ["250278","250423","250430","250531","250946","778519","250529","250887"]