As LotusLive Meetings/Engage is related to Sametime (LotusLive Meetings is the former Sametime Unyte), it is no surprise you can use it as chat server.
It is no big deal. Users of Lotus Notes 8.x or Lotus Sametime Connect only have to create a new Sametime Community.
Users of Notes versions earlier than 8 have to choose between their own community and LotusLive or have to install the instant messaging client (which is Sametime Connect - what a surprise ) you can download from LotusLive.
User name and password are - of course - those for LotusLive.
Host server is im.lotuslive.com - and port is 1533 (default).
Adding contacts is the same as always only that you have to choose the correct community and can only search for first- and/or lastname. Shortname or email address won't get you any search results.
Now you will be able to chat with customers and business partners. You will even see their community status within your inbox.
The world is growing together - yeah!
Only there is one little downer: this feature is only available for full and trial users. Guests won't be able to use it.