i need to develop this app that will need to initiate a voice call between two numbers...my understanding is somethiing like using skype java api to create the conference call but i am unable to use skype for some reason is there any other way or service that would provide such a service to satisfy this requirment
I assume that you will not implement a media server for the conference.
In this case you will need JAIN SIP stack (http://jsip.java.net/) and some media framework (JMF is a very good choice - http://www.oracle.com/technetwork/java/javase/tech/index-jsp-140239.html). You can see what the folks at SipCommunicator have done: http://sip-communicator.org/.
For the server side you might use Asterisk, Yate or similar.
If you have to implement also the server side then the things get a little more complicated. You can check Mobicents Media Server and Sip Servlets (http://www.mobicents.org)