VB.NET XML Processing a XMLNodeList with Namespace

OK based on the below code we Load the Doc and get the 3 Call Nodes. My question now is how can i do the folowing things

a) Get a list of all sub nodes of this node
If posible so i could loop thru that list
b) Check if a specific node exists
<NPInfo>
c) Access data in a subnode for example how would i access the
<OrigParty>
<SubscriberAddr type="e164">+12095551122</SubscriberAddr>
</OrigParty>

Imports System.Xml
Imports System.Xml.XPath

Dim m_xmld As XmlDocument
Dim m_nodelist As XmlNodeList
Dim m_node As XmlElement

'Create the XML Document
m_xmld = New XmlDocument()
'Load the Xml file
m_xmld.Load("sample2.xml")

'' Added these two lines
Dim nsmgr = New XmlNamespaceManager(m_xmld.NameTable)
nsmgr.AddNamespace("ns", "http://www.metaswitch.com/cfs/billing/V1.0")

'Get the list of name nodes
'' Modified your XPath and added the second parameter 
m_nodelist = m_xmld.SelectNodes("/ns:File/ns:CDRs/ns:Call", nsmgr)
'Loop through the nodes

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