The list of "servers" you get by default with NM were unplugged 20 months ago. MSN Messenger was integrated into NM's directory list (you can also start an NM conference via Messenger's UI as well). When opening the Directory, change the dropdown to "Microsoft Internet Directory" to see your Messenger buddy list, click someone who's logged on, and it connects...even if the other person doesn't currently have NM running (they accept via an automated Messenger dialog...pretty cool).
Be sure you're using build 3388 or later of NM for Messenger integration. You can download the L&G
here.
You can find dozens of public ILS servers
here...just enter them into NM's directory list. You can also create "speeddials" from NM's Call menu and email them to friends (as long as you have a static IP) for immediate "direct-dial" connections.
However, as with nearly all internet-aware apps, NM has problems with ICS. NM utilizes your IP address to place and receive calls. Plus, it uses SSL for encryption purposes, so it needs to know the MAC address of your NIC and stuff like that. Routers, ICS, etc, prevents proper behavior that most single-machine users enjoy. As long as your friend knows your IP address, he *might* be able to call you, but you definitely will not be able to call him until he has an IP address specifically assigned to his machine for 'net access, like you do (which means, no mo' ICS).