diff --git a/xep-0181.xml b/xep-0181.xml
index a292031a..398c4364 100644
--- a/xep-0181.xml
+++ b/xep-0181.xml
@@ -23,6 +23,12 @@
   <shortname>jingle-dtmf</shortname>
   &stpeter;
   &seanegan;
+  <revision>
+    <version>0.4</version>
+    <date>2006-10-31</date>
+    <initials>se/psa</initials>
+    <remark><p>Specified error handling and service discovery.</p></remark>
+  </revision>
   <revision>
     <version>0.3</version>
     <date>2006-07-12</date>
@@ -56,8 +62,7 @@
   <example caption="Basic DTMF Format"><![CDATA[
 <dtmf xmlns='http://jabber.org/protocol/info/dtmf'
       action='button-down'
-      code='integer'
-/>
+      code='integer'/>
   ]]></example>
   <p>The &lt;dtmf/&gt; element SHOULD possess one 'action' attribute, which MUST be either "button-up" or "button-down", specifying whether the button is being depressed or released. This allows DTMF tones to be reconstructed in real-time. If the 'action' attribute is not included, the recipient MUST assume this to be a "button-down" event, and imply a "button-up" event after a reasonable timeout (100 milliseconds is RECOMMENDED) or when another DMTF event is received.</p>
   <p>Unless, the 'action' attribute is 'button-up', the &lt;dmtf/&gt; element MUST possess a 'code' attribute that specifies the tone to be generated. The value of the 'code' attribute SHOULD be one the following characters: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, #, and *  -- however, the characters A, B, C, and D MAY be sent as well. <note>Although A, B, C, and D were originally defined as part of DTMF, they were never deployed to telephony consumers and were used only for control purposes at private branch exchanges (PBXs) and central office operator stations; however, they are used in certain non-telephony applications of DTMF, such as ham radio.</note></p>
@@ -73,14 +78,21 @@
           sid='a73sjjvkla37jfea'>
     <dtmf xmlns='http://jabber.org/protocol/jingle/info/dtmf'
           code='7'
-          action='button-up'
-    />
+          action='button-up'/>
   </jingle>
 </iq>
   ]]></example>
+  <p>The receiving entity MUST send an IQ result if it can process the DTMF:</p>
+  <example caption="Receiving Entity Acknowledges DTMF Message"><![CDATA[
+<iq from='ivr.shakespeare.lit'
+    from='juliet@capulet.com/balcony'
+    id='dtmf1'
+    type='result'/>
+  ]]></example>
+  <p>If the receiving entity does not understand or cannot process the payload, it MUST return an appropriate XMPP error (such as &unavailable; or &unexpected;).</p>
 </section1>
 <section1 topic='Negotiating RFC 2833' anchor='2833'>
- <p>Some applications may want to stream Jingle voice RTP directly to a non-XMPP entity, such as a SIP phone. In this scenario, DTMF needs to be sent in the content channel. Jingle DTMF allows to Jingle entities to negotiate whether to send RTP over the XMPP signalling channel as described above, or over the content channel, using RFC 2833.</p>
+ <p>Some applications may want to stream Jingle voice RTP directly to a non-XMPP entity, such as a SIP phone. In this scenario, DTMF needs to be sent in the content channel. Jingle DTMF enables Jingle entities to negotiate whether to send RTP over the XMPP signalling channel as described above, or over the content channel using RFC 2833.</p>
  <p>To request that the voice session switches to RFC 2833, a client sends a &lt;dtmf-method/&gt; element, qualified by the 'http://jabber.org/protocol/info/dmtf' namespace as the payload of a Jingle content-info message:</p>
  <example caption="Client requests using RFC 2833"><![CDATA[
 <iq from='juliet@capulet.com/balcony'
@@ -117,17 +129,28 @@
  ]]></example>
 </section1>
 
+<section1 topic='Service Discovery' anchor='disco'>
+  <p>If an entity supports Jingle DTMF (which natively includes sending of DTMF in the XMPP signalling channel), it MUST return a &xep0030; feature of "http://jabber.org/protocol/jingle/info/dtmf" in response to service discovery information requests.</p>
+  <p>If an entity also supports sending of DTMF in the content channel, it MUST also return a service discovery feature of "http://jabber.org/protocol/jingle/info/dtmf#rtp" in response to service discovery information requests.</p>
+</section1>
+
 <section1 topic='Security Considerations' anchor='security'>
   <p>This document introduces no known security vulnerabilities.</p>
 </section1>
+
 <section1 topic='IANA Considerations' anchor='iana'>
   <p>This document requires no interaction with &IANA;.</p>
 </section1>
+
 <section1 topic='XMPP Registrar Considerations' anchor='registrar'>
   <section2 topic='Protocol Namespaces' anchor='registrar-ns'>
     <p>The &REGISTRAR; shall include 'http://jabber.org/protocol/jingle/info/dtmf' in its registry of protocol namespaces.</p>
   </section2>
+  <section2 topic='Service Discovery Features' anchor='registrar-disco'>
+    <p>The XMPP Registrar shall include 'http://jabber.org/protocol/jingle/info/dtmf#rtp' in its registry of service discovery features.</p>
+  </section2>
 </section1>
+
 <section1 topic='XML Schema' anchor='schema'>
   <code><![CDATA[
 <?xml version='1.0' encoding='UTF-8'?>