First of all thanks for your answers guys!

I'm aiming to audio conf.

Emrah, last few questions - which method do you use for conference merging? Conference bridge? I mean - I want to allow users to send commands over DTMF. 
In that case I suppose I must catch DTMF and execute conference commands on another layer using ESL. Maybe you know another concept?
Also I don't really understand - do I really must use FS as SBC-  due to some conference layer may be there - or can I use Kamailio (as i'm used to that very much)?
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