We have three offices in different cities. Each office is connected with a T1 internet connection and the computers in the offices connect to the internet through a Linux server using NAT.
We want to install IP phone for each computer. So that the users in one office can talk to users in other offices as well as with them. We will be using IP phone sets from any company.
What I wanted to know, is it possible for users at one site, behind a NAT will be able to talk to users on other side of the NAT without VLAN?
Can we setup exchange or something for that using Linux server without using any hardware gateway or such?
And lastly, can our users get calls from any user on outside our networks who is using any net telephony service like net2phone or ICQ individually?
Thanks in advance.