Yea im a newbie to and installed trixbox recently, (i also opted for version 2.6 as the concensus seems to be avoid 2.8 until the bugs are ironed out.) Note this is a distro so your hardrive will be wiped and OS replaced with CentOS 5.x. and when you boot it up theres no X Windows just a command prompt
The idea is you instal Trixbox on a spare PC on a LAN, then point a webbrowser from another PC to it to access the web admin which gives your a gui to set everything up on.
Ive never heard of 'optimum online triple play', i presume its a voip provider, if youve got a sip account or iax account with them you can setup asterisk to connect to it. You may or may not be able to have multiple calls at the one time, depends on your voip provider and account. Also, bandwidth/quality of your internet connection would come into play here, search for voip test on google for a java simulation test.
You can then instal a softphone such as the free X-Lite on all the PCs on the LAN, point it to your asterisk server's ip so you can use it as a phone with an standard PC headset.
There may be a way to instal Trixbox without the distro, though you'd also need to check it will work on Ubunto.
Support forums are very responsive at
I followed a community guide to set mine up called Trixbox 2 Without Tears, skipping the extra features i did not need.
The web admin Trixbox actually uses is a software package called FreePBX, another open source project for managing asterisk config.
Alternatively you may want to setup the asterisk software itself on your ubuntu, this would be beyond me as im not a linux guy, but O'Reilly have a free book on Asterisk, see the html version at
(about version 1.4 of Asterisk)