Wisconsin is currently a one-party state though recent attempts in the legislature there have attempted, unsuccessfully so far, to change it to two-party. Even so, any evidence gathered by a one-party consensual recording is inadmissible except in murder or drug cases, as they say.
The Wisconsin Stats 885.365 Recorded telephone conversation (1) states "Evidence obtained as the result of the use of voice recording equipment for recording of telephone conversations, by way of interception of a communication or in any other number, shall be totally inadmissible in the court of this state in civil actions, except as provided by 968.28 to 968.37." Exceptions are it the party is informed before the recording is informed at the time that the conversation is being recorded and that any evidence thereby obtained may be used in a court of law or such recording is made through a recorder connector proved by the telecommunications utility as defined in WI Stats 968.28 - 968.37 (which is the stat for court ordered wiretaps) which automatically produces a distinctive recorder tone that is repeated at intervals of approximately 15 seconds. Fire department or law enforcement agencies are exempt as are court ordered wire tapes.
Also a recording on the phone made from a out of state call or made to an out of state party, has to have the party informed of the recording and his consent or the tone on line, every 15 seconds, or a consent in writing before the recording is started.
Needless to say this does not allow a person not a party to the conversation to record any part of the conversation without the parties to the conversation being informed the third party is recording the conversation.