VoIP scenario

Hi

Consider a VoIP scenario.
There is a central SIP server (openser/asterisk/ any sip server) hosted on
a public ip (integrated with a domain xyz.com or hosted along with a web server).
Main motive is IP calling only .(no GSM or PSTN calling required)

It shud support NAT transversal and simple authuntication based on username and password.

At Client side

1) There are few nodes under a firewall with static ip(61.11.x.x), few of them using softphone
and few are with ATA(analog telephone adapter)

2) There shud be sum integatraion with website , web based ip 2 ip calling .

Sum web based VoIP applet dat can do ip2ip/sip calling.

3) SIP client on Mobile/PDA (java applet or symbian) n sip calling using GPRS.

4) sip chating (optional*)


Registeration

4 feilds required
Name(Username) ,password, sip extention 4 digit and email id.

MAIN NEED
The main need is of voice mail.
If d user is not available (offline mode) there shud be IVR to callie asking for recording the message.
And immedately the recored message (in mp3 format ) shud be mailed to the corresponding email id.
Voicemail is quite important.


Need help..!
How to proceed with the things, wat to use , how to use..!


Regards
PoPo
Kapil888 [!at] ****** (replace the [!at] with a @)

Asterisk is probably the easiest option to do what you want