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It’s a basic right of privacy to assume that when you’re on the telephone, no one is listening except the person you’re speaking with. In the United States, history abounds with examples when this right was transgressed (we all remember Watergate, right?) and so, if situations do arise when civilian calls are recorded, laws exist to help identify when and under what circumstances such recording is permitted.

For most developed democracies, recording of telephone conversations is strictly regulated in order to safeguard the privacy of telephone users. In the United States, for example, Federal call recording laws require that at least one party taking part in the call be notified of the recording (18 U.S.C. §2511(2)(d)). In most cases, that’s covered by those “This call may be monitored for training and quality control purposes” disclaimers during customer service calls.
Outside of the United States, laws differ significantly by country:

Australia: Australia’s federal Telecommunications (Interception and Access) Act of 1979 call recording laws dictates that if a call is to be recorded or monitored, an organization must tell you at the beginning of the conversation so that you have the chance either to end the call or ask to be transferred to another line where monitoring or recording does not take place (if this is available).

Canada: Organizations subject to the Canadian Personal Information Protection and Electronic Documents Act (PIPEDA) must comply with the following rules when recording conversations:

1. The individual must be informed that the conversation is being recorded at the beginning of the call. This can be done by an automated recording or by a customer service representative. 
2. The individual must be advised of the purposes of the recording, and the organization must be clear about its purposes. An organization should not state that it is recording the conversation for quality assurance purposes if, in fact, the recording will be used for other reasons. If the individual proceeds knowing the conversation is being recorded and the purpose of the recording, consent is implied. 
3. If the caller objects to the recording, the organization should provide the caller with meaningful alternatives, including not taping the call, visiting a retail outlet, writing a letter, or conducting the transaction over the Internet.

Denmark: Call recording is legal by any active participant, with no requirement to make other parties aware of the recording. However, forwarding or playing calls considered private is illegal.

Finland: Recording of calls by a company or an employer is subject to data protection legislation and, in general, requires informing the participants prior to recording.
Germany: Germany is a two-party consent state, meaning that telephone recording without the consent of the two or (when applicable) more parties is a criminal offense according to Sec. 201 of the German Criminal Code.

Romania: The recording of a conversation by a private member to that conversation is specifically permitted. Nevertheless, while such recordings are legal, making use of them may fall subject to further civil or criminal law.

United Kingdom: Under the Regulation of Investigatory Powers Act of 2000, a recording made by one party to a phone call without notifying the other is not prohibited provided that the recording is for their own use. Recording without notification is prohibited where some of the contents of the communication are made available to a third party. Businesses are allowed to record with the knowledge of their employees, but without notifying the other party...

1. to provide evidence of a business transaction
2. to ensure that a business complies with regulatory procedures
3. to see that quality standards or targets are met
4. to protect national security
5. to prevent or detect crime, among other things.