Federal law permits recording of telephone conversations as long as one party consents to having his voice recorded. Therefore, it is legal under federal law for someone to record conversations in which they are participating, reports the Digital Media Law Project. However, state laws on recording telephone calls vary.
Most states are "one-party consent" states, meaning that one person can record telephone calls they have with another person. However, 11 of the 50 states require both parties to be informed that the call is being recorded. CallCorder.com has a list of all of the states that require two-party consent. In a two-party consent state, recording a call without the other person's knowledge is a crime. In California, for example, the punishment may include a fine of up to $2,500, imprisonment for up to one year, or both.