This is an excerpt from http://www.aapsonline.org/judicial/telephone.htm
Wisconsin Wis. Stat Ann. §§968.31(c) &885.365(1) It is lawful to intercept a communication if one is a party to the communication or has received the prior consent of a party to the communication. But, another section of the Wisconsin code states that evidence obtained by recording telephone conversations shall be totally inadmissible in civil actions in the courts of Wisconsin.
Of course, you must confirm this with a local attorney.
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I agree with Attorney Sargeant, you should speak with a local attorney. I assume that you are seeking to record a conversation with another person in Wisconsin. However if the conversation takes place in another state or is over the phone with someone in another state, different laws may apply.
I am not your attorney, and my responses on Avvo should not be considered legal advice.