FIELD OF THE INVENTION The present invention relates to communication systems in general, and in particular, a voice messaging system which utilizes time-of-call information from caller ID or ANI information in the storage, selection and retrieval of voice messages.

BACKGROUND OF THE INVENTION The storage, selection and retrieval of voice messages is well known. Such systems are disclosed in, for example, U. S. Patents Nos. 5,283,818,5,390,236,5,524,140 and 5,572,576, the contents of which are incorporated herein by reference.

One type of voice messaging system dispenses with the need to have individual storage and retrieval units located at each subscriber location. Instead, a common voice message system is used for a number of subscribers, and each stored message is identified as being associated with a particular subscriber to facilitate the proper storage and retrieval of messages for each subscriber.

Still other types of voice messaging systems, such as those disclosed in the above-identified patents, allow a user to selectively retrieve a particular message without having to listen to each message. This is accomplished by maintaining a linking code to associate the message information (e. g., name, telephone number) with the stored voice message.

This type of approach is possible because the message information and the messages themselves are stored in the same location, i. e., the user's voice messaging unit or at the central voice mail system. However, when the voice message is stored at a central location and the message information is only available at a remote display terminal, there is no way to associate the two types of information stored in different locations. The present invention provides such an association.

SUMMARY OF THE INVENTION The present invention is directed to a centralized voice messaging system which allows the selective retrieval of voice messages by a number of users. The message information is stored in each individual user location (e. g., cellular phone, smart phone) while the voice messages are stored in a central storage unit. Although the message and the message information are stored in separate locations, an association between them is maintained using caller ID information, as well as synchronized time-of-call information.

Specifically, according to the present invention, when a call is received at the user terminal, the caller ID information, including time of call, is extracted and stored.

If the call is to be processed by the centralized voice messaging system (i. e., the calling party is to leave a message), the call is transferred to the voice messaging system where the voice message is stored. At the voice messaging system, the system stamps each message with a time stamp in accordance with a clock which is preferably synchronized to the caller ID time-of-call information which has been stored in the user terminal.

In order to retrieve messages, the user is presented with the call information for the received calls. This call

information typically includes the name of the calling party, as well as the time of the call. Such information is typically provided by way of the caller ID information transmitted as part of the incoming call. After reviewing the call information, the user may select a particular voice message to listen to, with the message being retrieved from the centralized voice message storage system.

In order to retrieve a selected message from the central storage unit, the user terminal transmits to the central storage unit the time corresponding to the selected message. The central storage unit receives this time, and having maintained its own time stamp for each stored message, it is able to retrieve the stored message and transmit it to the user terminal for playback to the user. In this way, although the message information which is displayed to the user and the actual stored messages are located in different locations with no direct association between them, an association is actually maintained using the time portion of the caller ID information at the user terminal, and the time stamp at the central message storage location. It should be noted that the time-based message retrieval may allow for a certain tolerance between the time-of-call information at the user terminal and the time-of-call information at the central storage unit, i. e., the time matching does not have to be exact.

Additionally, the user terminal may tag, or otherwise identify, the stored message information to indicate which callers actually left a voice message. This information is used in the subsequent retrieval of messages to indicate to the user which of the callers actually left messages. This is achieved using the confirmation information which is transmitted from the central storage unit to the user terminal to confirm the storage of each voice message. In this way, the user terminal simply tags the most recently received message information once the confirmation information is received.

Since message information is maintained at the user terminal for each received call, not just those calls for which messages are stored, there exists the possible situation where two or

more calls are received but a message is left only for the first of the calls. In this case, the user terminal might possibly erroneously assign the voice message stored tag to the wrong message information. In order to avoid this problem, the tagging is performed only if the confirmation is received within a certain prescribed time limit of the message information, assuring that the tag is properly related to the message information for that call, not a different call.

Other features and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings which illustrate, by way of example, the features of the present invention.

DESCRIPTION OF THE DRAWINGS Figure 1 is a block diagram of a voice messaging system according to the present invention; Figure 2 is a flowchart for message storage; Figure 3 is a flowchart for message retrieval; and Figure 4 is a schematic diagram of a display included in a called terminal of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to Figure 1, there is shown a block diagram of a time-matched voice messaging system according to the present invention. Typically, a calling terminal 12 will call a called terminal 14, and if the call is not answered or picked up at the called terminal 14, the call is transferred to a voice message system 10 where a voice message may be left by the calling terminal 12. When the call is first received at the called terminal 14, caller ID information, including the time of call, is extracted and stored at the called terminal 14. Similarly, after the call is transferred to the voice message system, it is also time stamped in accordance with a clock which is preferably synchronized to the caller ID information stored at the called terminal 14.

The called terminal 14 preferably includes a display 16 (FIG. 4) that displays the caller identification

information, time-of-call information, and message information, as described in greater detail below. The called terminal preferably also includes plural selection buttons 18 to allow a user to select a corresponding call for message playback.

Alternatively, one or more of the standard keypad buttons on the called terminal could serve as selection buttons when the called terminal is in a message retrieval mode, as described in greater detail below. The called terminal also includes circuitry, preferably in the form of a processor or controller, the function of which is set forth in detail below in connection with Figures 2 and 3.

The process of storing voice messages is illustrated in the flowchart of Figure 2. Beginning at step 20, operation begins when an incoming call from a calling terminal 12 is detected. The incoming call signal includes caller identification information and time-of-call information, such information typically being transmitted between the first and second rings as is well known in the art. Alternatively, the called terminal 14 may include an internal clock which supplies the time-of-call information. Operation then proceeds to step 22, and the caller identification information and time-of-call information are stored and preferably displayed by the called terminal 14 on the display 16. Then, at step 24, the called terminal 14 determines whether the call is answered, by detecting whether the called terminal is off-hook. If so, operation flows to step 26, and the called terminal waits for an on-hook condition indicating the end of the call. Once that occurs, operation proceeds back to step 20 and the called terminal waits for the next incoming call.

If the call is not answered at step 24, operation proceeds to step 28, and the called terminal 14 determines whether a preselected ring limit has been exceeded. For example, the called terminal may be programmed to ring four times (or some other number of times) before the call is routed to the voice message system 10. If the ring limit is exceeded, operation flows to step 30, and the called terminal 14 transfers the call to the voice message system 10, where the caller is prompted to leave a message for the called party.

If the caller leaves a voice message, that message is stored in the memory of the voice message system along with a time stamp generated by the voice message system. Alternatively, the called terminal may transmit the time-of-call information to the voice message system. In one illustrative embodiment, the voice message system then transmits a confirmation signal back to the called terminal 14 indicating that the caller left a message. The called terminal stores that information and associates it with the caller identification information and time-of-call information for that call. Such information is preferably displayed on the display 16 of the called terminal 14 (FIG. 4). Operation then proceeds back to step 20 to detect the next incoming call and repeat the process.

Referring to FIG. 3, the process of retrieving voice messages is illustrated. At step 50, the called terminal 14 determines whether the user has directed the called terminal to retrieve a message. This can be done by depressing a particular button 19 on the called terminal corresponding to a message retrieval mode, such that the terminal enters a message retrieval mode. If the user has selected the call retrieval mode, operation proceeds to step 52, and the called terminal displays the call information on the display 16, which preferably includes the caller identification information, time-of-call information, and message confirmation information.

Alternatively, the called terminal can be programmed such that the display 16 continuously displays the call information, such that the user can direct the called terminal-to retrieve a message by simply pressing one of the selection buttons 18, without the called terminal having to first enter a message retrieval mode.

In any event, operation then flows to step 54, and the called terminal determines whether one of the messages has been selected for play back. This is preferably done by monitoring whether one of the selection buttons 18 has been depressed. If no button is depressed, operation proceeds to step 56, and the called terminal determines whether a preset time limit for making the selection has expired. If so,

operation proceeds back to step 50. If not, operation proceeds back to step 54.

Once the user selects a message for play back, at step 58 the called terminal 14 retrieves the time-of-call information for the selected call, and at step 60 the called terminal transmits a request signal to the voice message system 10, the signal including the retrieved time-of-call information. The voice message system 10 receives the signal from the called terminal and uses the time-of-call information to find and retrieve the corresponding message from its data store. It will be apparent that the voice message system 10 may use the time-of-call information to retrieve the message with the closest time stamp, and that the time stamp and time- of-call information do not need to be identical. At step 62, the voice message system 10 transmits the retrieved voice message to the called terminal, which then plays the selected voice message to the user, at step 64.

While several forms of the invention have been described, it will be apparent to those skilled in the art that various modifications and improvements may be made without departing from the spirit and scope of the invention.