Any specific record retention requirement for recordings will exist only at the state level. Check with your state bankers association or department of financial institutions to see if they maintain a list of all record retention requirements.
There may not be any state record retention requirement for recordings, primarily because there is no requirement that the calls be recorded. More likely than not, this an internal control that you established for your own protection. If so, then the length of record retention is based on your tolerance for risk.