According to the documents, Assange claims to have phone call recordings from Althingi, the Icelandic parliament, but this is the first time that the existence of such data is mentioned publicly.
The recordings are mentioned twice, but they are from March 2010. "We now have phone call recordings for the past four months" said Assange. "Yes, you told me before", answered Manning, according to the documents.
The credibility of these documents is unclear, and it is relatively easy to forge such documents. It is also not known how anybody could obtain phone call recordings from the office phones in parliament. There is nothing that indicates that the parliament records phone calls.
According to Icelandic laws, it is required to inform the person you are speaking with if the phone call is being recorded. Given that the parliament is not violating laws it is clear that Assange or his associates would have to have installed recording devices or wiretaps in the parliament.