Ring group with conference

I have a requirement for conference in which it should work by inviting callers to join a conference. In detail, from any station i will dial a conference number, it will ring in corresponding stations and at all stations after they lift the handset, the conversation should get into a conference call… Will it be possible by version i have installed. Asterisk with Free pbx 2.5.2… If so, how is it possible?? Help me out pls…

First of all you have a very old version of Asterisk and FreePBX, you need to update. Also those versions are very suspect, is this actually a trixbox?

What you want is quite simple to write a custom extension in Asterisk to perform.