If you think it should be against the law for one person in a conversation (telephone or otherwise) to record another person--without disclosing they are recording--then please sign this petition. 

Missouri Statue allows phone (or other) conversations to be recorded as long as one person (e.g. the person making the recording) gives prior consent.  The person on the other end does not have to be told or give consent for their conversation to be recorded.  There are certain reasons that recordings are not allowed, but there are times when your conversations can be recorded without you knowing, and this is considered legal.  

Here is the full MO Statute (Scroll down to Section 2, to see where recording conversations is legal): 

542.402.  Penalty for illegal wiretapping, permitted activities. — 1.  Except as otherwise specifically provided in sections 542.400 to 542.422, a person is guilty of a class E felony and upon conviction shall be punished as provided by law, if such person:

  (1)  Knowingly intercepts, endeavors to intercept, or procures any other person to intercept or endeavor to intercept, any wire communication;

  (2)  Knowingly uses, endeavors to use, or procures any other person to use or endeavor to use any electronic, mechanical, or other device to intercept any oral communication when such device transmits communications by radio or interferes with the transmission of such communication; provided, however, that nothing in sections 542.400 to 542.422 shall be construed to prohibit the use by law enforcement officers of body microphones and transmitters in undercover investigations for the acquisition of evidence and the protection of law enforcement officers and others working under their direction in such investigations;

  (3)  Knowingly discloses, or endeavors to disclose, to any other person the contents of any wire communication, when he knows or has reason to know that the information was obtained through the interception of a wire communication in violation of this subsection; or

  (4)  Knowingly uses, or endeavors to use, the contents of any wire communication, when he knows or has reason to know that the information was obtained through the interception of a wire communication in violation of this subsection.

  2.  It is not unlawful under the provisions of sections 542.400 to 542.422:

 (1)  For an operator of a switchboard, or an officer, employee, or agent of any communication common carrier, whose facilities are used in the transmission of a wire communication, to intercept, disclose, or use that communication in the normal course of his employment while engaged in any activity which is a necessary incident to the rendition of his service or to the protection of the rights or property of the carrier of such communication, however, communication common carriers shall not utilize service observing or random monitoring except for mechanical or service quality control checks;

  (2)  For a person acting under law to intercept a wire or oral communication, where such person is a party to the communication or where one of the parties to the communication has given prior consent to such interception;

  (3)  For a person not acting under law to intercept a wire communication where such person is a party to the communication or where one of the parties to the communication has given prior consent to such interception unless such communication is intercepted for the purpose of committing any criminal or tortious act.