The xml namespace descriptors are bulky. The rest looks efficient, for xml, and almost readable with some indentation.

  <?xml version="1.0" encoding="UTF-8"?>
  <json:object xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
               xmlns:json="http://www.ibm.com/xmlns/prod/2009/jsonx"
               xsi:schemaLocation="http://www.datapower.com/schemas/json jsonx.xsd">
    <json:string name="name">John Smith</json:string>
    <json:object name="address">
      <json:string name="streetAddress">21 2nd Street</json:string>
      <json:string name="city">New York</json:string>
      <json:string name="state">NY</json:string>
      <json:number name="postalCode">10021</json:number>
    </json:object>
    <json:array name="phoneNumbers">
      <json:string>212 555-1111</json:string>
      <json:string>212 555-2222</json:string>
    </json:array>
    <json:null name="additionalInfo"/>
    <json:boolean name="remote">false</json:boolean>
    <json:number name="height">62.4</json:number>
    <json:string name="ficoScore"> &gt; 640</json:string>
  </json:object>

translated (by hand) into JSON gives

  {
    "name": "John Smith",
    "address": { "streetAddress": "21 2nd Street",
                 "city": "New York",
                 "state": "NY",
                 "postalCode": 10021
               },
    "phoneNumbers": ["212 555-1111", "212 555-2222"],
    "additionalInfo": null,
    "remote": false,
    "height": 62.4,
    "ficoScore": " > 640"
  }