Question: I wanted to add a voice chat feature to my business app. I have been trying hard to find anything useful but there is not much help regarding this. Could anyone plz point me to something concrete??

PS: The skype app makes use of this feature.

Answer: 
This is a lot of work as there is no "built in" sdk features or third party off the self components that will help you do it without a lot of work on your end.
Your options (as far as I know) are:

* Build your own solution.
* Look for a third party solution.
* Look for a open source solution.

Voice "chat" could be one of many things like:

* using the voice features of a cellular network to a conference call.
* using the voice features of a cellular network with a PBX server that supports conference calls.
* using a [VOIP](http://en.wikipedia.org/wiki/Voice_over_Internet_Protocol) solution using a [SIP](http://en.wikipedia.org/wiki/Session_Initiation_Protocol) stack with a SIP server
* using a [XMPP](http://xmpp.org/) [Jingle](http://en.wikipedia.org/wiki/Jingle_%28protocol%29) solution (I believe the google voice service uses this)
* using your own SIP setup solution
* custom solution

None of these options are easy. 

Open Source SIP implementations that have iphone ports (that I know of):

* [reSIProcate](http://www.resiprocate.org/Main_Page)
* [pjsip](http://www.pjsip.org/)

Update:

SIP & Jingle both use [RTP](http://en.wikipedia.org/wiki/Real-time_Transport_Protocol) for the actual transport protocol between the parties. RTP is a UDP point-to-point protocol. The ports which form a session are negotiated using other protocols such as RTSP (using SDP in the setup method) and SIP. RTP and RTCP typically use unprivileged UDP ports (1024 to 65535).
For easy Server / Client setup check [Jingle Nodes](http://jinglenodes.org) in combination with SIP Communicator which is a Desktop application. But as being opensource I presume you can reuse a lot of the code to make it mobile. Specially for Android. Check this draft of a [Jingle Nodes Setup Guide](https://docs.google.com/present/edit?id=0AYRjaHIDbVEcZG52cmd3N180NzVrc201Z2JmYw&hl=en)