When implementing LCS 2005 with the public IM connectivity feature, there are a couple extra steps to take to be able to add MSN IM accounts to your Communicator client. First I want to touch on what happens when you implement LCS and MSN IM accounts associated with your corporate domain.
Converting Corpdomain.com Accounts
Some users in your company will inevitably create MSN IM accounts using their work email address (e.g. firstname.lastname@example.org). Once you implement PIC (public IM connectivity) with LCS for corpdomain.com, users can no longer login to MSN Messgner with their IM account. This is not a big deal if the LCS implementation occurs over a weekend and there is no downtime to the users. The users simply re-add their contacts to the Communicator client and start using this as their IM client. However, the users may want to maintain a separate IM account with all their contacts with no disruption. The users need to convert their corpdomain.com IM accounts to a MS account. The following article provides good instructions on how to convert the IM account to a messengeruser.com or msn.com account. In theory, you wait an hour after conversion and once all your contacts login again, their contacts lists reflect your new account. I have seen sporadic issues with this process which I'll cover in a different entry.
EASI accounts are IM/Passport accounts using non-Microsoft owned domains. Until recently, you could not add IM accounts to Communicator that were EASI accounts. There is a good article on issues with EASI accounts and PIC.
Today, Jeremy Buch (Microsoft), responded in a community thread where I posed the question about when EASI accounts would be supported. According to him, they are supported. There is a slight variation when adding a contact with an EASI account. Instead of adding the account as will@ personldomain.com, you add the account as will(personaldomain.com)@msn.com. This applies to adding the account from outside the MSN cloud or from your LCS implementation using Communicator. If you are using MSN Messenger, add the contact using the email address.