Righty. I can get the information via xml to my service - but how I reply with xml too?

VB Code:
  1. <WebMethod()> _

  2.     Public Function AcceptSMS(ByVal oanumber As String, ByVal danumber As String, ByVal udstring As String) As String

  3.         Dim strRetVal As String = ""

  4.         strRetVal = "Passed data : <br>"

  5.         strRetVal &= oanumber & "<br>"

  6.         strRetVal &= danumber & "<br>"

  7.         strRetVal &= udstring & "<br>"

  8.         Return strRetVal

  9.     End Function

That will reply with just text, but I need to format it in proper xml. How do I reply properly...?