Currently we have asterisk 1.4 installed in a low end server. My doubt is what is the concurrent calls and extensions limitation that asterisk can support? Please advice and sorry if post at wrong place or someone had asked this before.
Thanks 
Hi
There is no definitive answer to this and it is asked often and in most cases important information is left out of the question which makes it even harder to answer. For example you say a “low end server” but you dont say the spec of it and you dont say how many extensions you have and how many concurrent calls you expect, and what applications you are expecting to run as well.
So you can see its not really possible to answer even if we wanted to.
There is lots of anecdotal evidence on the voip-info wiki on sizing of servers though.
Ian