One of the finest features of the example demo configuration is the ready made voicemail system, brought to you by mod_voicemail. The last four actions in "Local_Extension" in demo dialplan are as follows:

        <action application="bridge" data="user/${dialed_extension}@${domain_name}"/> 
        <action application="answer"/> 
        <action application="sleep" data="1000"/> 
        <action application="bridge" data="loopback/app=voicemail:default ${domain_name} ${dialed_extension}"/> 

This means: try to connect the incoming call to the callee (that is, to the dialed_extension, that was derived from destination_number), if you fail to connect it (eg, the phone(s) at dialed_extension is/are not answered before the 30 second timeout), then answer the incoming call (eg, go off hook), wait for 1 second doing nothing, then connect that incoming call to the voicemail application (using the loopback "fake" endpoint).

After an incoming call gets connected to the voicemail application, and the caller left a message, FreeSWITCH is smart enough to light up (or blink) the MWI (Message Wait Indicator) on the callee phone(s). Wooot, that kind of magic gives a lot of satisfaction to us telco geeks. (Also, when the voice message has been heard or deleted by callee, FreeSWITCH will have those MWIs to shut. Yay!):

Let's see an example using Jitsi, a fine free and open source softphone. If the callee, when she's back at the softphone, clicks on the red icon with the number 4 (eg, the MWI says: "you have 4 messages waiting"), she will see some details about the voicemail, eg only 3 of the 4 messages are new:

Then, when she try to hear the message, she hit a bug in Jitsi (version 2.10.5550 for Linux). Do to that bug, when she clicks the blue handset icon, she actually call back herself (that is, she call back the account the messages where left for).

So, if she actually want to hear the messages, she have to call *98 (or 4000) from the dialpad. She will be asked for her voicemail password. In default demo configuration, voicemail password is the same as the extension number. So, in this case is 1011. She will then have the whole panoply of a super featured voicemail system. And after all messages will be listened to, MWI icon will disappear. But let's see only some of the available options when she call *98 or 4000 to check her own voice mailbox:

Main menu: 
1-Listen to new messages 
2-Listen to saved messages 
5-Options menu (record name, record greetings, manage greetings, and so on) 
#-Exit voicemail 
While listening to a message: 
1-Replay message from the beginning 
2-Save message 
4-Rewind 
6-Fast-forward 
After listening to a message: 
0-Replay message from the beginning 
2-Save message 
4-Send to e-mail (requires configuration) 
5 - Return the call 
7-Delete message 
8 - Forward the voicemail message 

All those menus, and much more, are completely configurable by editing the XML file /usr/local/freeswitch/conf/autoload_configs/voicemail.conf.xml.

Also if you don't want to change it, give it a look. You'll discover much more options than described here. Also, don't forget to check our online documentation at http://freeswitch.org/confluence for more configuration, for setting up voicemail to mail (that is, voice message delivered to your mailbox as a mail attachment), and many more interesting features.