This should be possible, I briefly looked at http://www.exetel.com.au/voip_pdf/nb9wMaxx.pdf
and then looked at a page I set up for a phone on the wiki http://wiki.linuxmce.org/index.php/EP-636_SIP_Phone
and between those two you should be able to work out how to set up your phone/ata to work with LMCE.
You also need to set up your provider to work with Asterisk. One thing I will warn you about is security. I was hacked using Asterisk with 08.10 luckily as was on a pay as you go plan and it cost me less than 10GBP, others were not so lucky. One suggestion people have had is adding fail2ban http://wiki.linuxmce.org/index.php/Fail2ban_-_A_tool_against_brute_force
- I have no personal experience of this just giving you things to look at.