Every state has different laws when it comes to recording telephone conversations. Some states require that both/all parties consent to being recorded. Other states only require one party to consent to a recording. Here are some scenarios:

A)     All parties live in an all-party-consent state: All callers and parties being called have to be aware that the phone call is being recorded
B)     All parties live in a one-party-consent state: Only one party, whether it be the caller or the recipient of the phone call, need be aware that the call is being recorded
C)     One party lives in an all-party-consent state and one party lives in a one-party-consent state: Both parties must by which ever state has the more strict laws. It is advisable that the party recording get consent from the party they're calling

This is the list of states that only require one party to have consent to a recording:

Alaska Kentucky New York Texas
Arkansas Louisiana North Carolina Utah
Colorado Maine North Dakota Vermont
District of Columbia Minnesota Ohio Virginia
Georgia Mississippi Oklahoma West Virginia
Hawaii Missouri Oregon Wisconsin
Idaho Nebraska Rhode Island Wyoming
Indiana Nevada South Carolina  
Iowa New Jersey South Dakota  
Kansas New Mexico Tennessee  

This is the list of states that require both parties to consent to a recording:

California*
Connecticut
Delaware
Florida
Illinois
Maryland
Massachusetts
Michigan
Montana
New Hampshire
Pennsylvania
Washington

*California allows all-party-consent to be voided, and one-party-consent to become law-abiding, only if conversations about illegal activities are being recordeds