That's why most Customer Service centers play that message letting you know that your call may be monitored or recorded for training purposes. They're required to let you know that up front, by law.
As @jonny mentioned, there are definitely some states which require notification to one party on the phone call ( which if you were on the call can be just you), whereas other states are what are known as a two-party notification state which means that all parties must be aware that the phone call is being recorded. You break either of those laws depending on which state you're in and its a state crime. This is why many cellphone manufacturers have blocked phone call recording altogether.