if you use a2billing for your device2phone and peer2peer,and did calls when PSTN call the sip device from did calls or other sip friend call the sip device, if called is unavailable,or busy ,you may want the call goto voicemail,so caller can record voicemail,and voicemal will be sent to called's emai.

1. you must use asterisk realtime architecture ,because you cannot add 1000+ lines in voicemail.conf by hand,so I use mysql and cron job

CREATE TABLE `voicemail_users` (
`uniqueid` int(11) NOT NULL auto_increment,
`customer_id` int(11) NOT NULL default '0',
`context` varchar(50) NOT NULL default '',
`mailbox` varchar(15) NOT NULL default '0',
`password` varchar(4) NOT NULL default '8888',
`fullname` varchar(50) NOT NULL default '',
`email` varchar(50) NOT NULL default '',
`pager` varchar(50) NOT NULL default '',
`stamp` timestamp(14) NOT NULL,
PRIMARY KEY (`uniqueid`),
KEY `mailbox_context` (`mailbox`,`context`)
) TYPE=MyISAM;

The Asterisk open-source IP PBX is popular for several very good reasons, including its low cost, flexibility and powerful feature set. Another factor that draws many businesses to Asterisk is the ability to enhance the product with an array of add-on features and utilities. Many of these offerings are available at no cost (although some developers request a modest donation). These eight free add-ons will help you monitor, configure and use Asterisk in a variety of different ways.

Conference Calling in Business Today

            In the world of today, organizations have the advantage of using talent from all parts of the world. Companies that are larger, which have a greater infrastructure, and which have made their presence felt globally are especially aware of the problems of having to manage a diversified workforce.

With the rise of globalization it has become possible for companies to draw their workers from all parts of the world. This is an essential feature of companies trying to develop a worldwide influence. As a result, different departments and divisions may have separate commands. But the need to send out a single message does arise from time to time, and this is where the conference call becomes so very important.

The Magic of Video Conferencing

                  Video conferencing facilitates learning by allowing remote or distant learners to meet regardless of their location. Students can take classes at multiple universities. In essence classes that are not available at one location may be available at another through video conferencing. Video conferencing can also benefit non traditional students who are not able to attend classes during normal hours.

There are various types of videoconferencing; which is suitable for your application will depend upon the IT structure available and what it is that you actually want to achieve. Video conferencing has in the past been relatively expensive, but prices are coming down and it is possible for anyone with a fast enough internet connection to operate a video conference.

Installing asterisk

              You can install Asterisk in different ways. I will show you how you can download the source code and compile Asterisk yourself.Most open source projects use a cvs (Concurrent Versions System) to keep track of their code, and you can always download the latest version from there.