To configure your VOIP account with LinuxMCE, you need to go to 'Setup Wizard' (from the main menu, click on Advanced / Setup Wizard / House Setup / VOIP Provider. You will find your provider in the list. You have to enter your: - VOIP number, username and password obtained from your provider, then save the settings and reload the router.
You can find the Asterisk configuration page (AMP) by accessing the web admin (type your Core's IP in a browser), and go to Advanced / Configuration / Phones Setup. Here you can make changes to your provider's settings in the Trunk section, or setup different rules for calling in 'Inbound / Outbound routing'.
Hope this helps