Names used in iChat or the Messages Beta to Login to one of the services, sometime referred to as IDs in some cases.
iChat (or the Messages Beta) can log in to the AIM servers, the Jabber servers and in iChat 6 the Yahoo Servers.
To do the first of these it needs a valid AIM Screen Name.
These can com from registering with AIM, having Apple IDs that end with @mac.com or @me.com or in some cases some United States ISP email are also valid AIM Screen Names.
iChat 4 and 5 used to have a Button that linked to the @mac.com registration page or the AIM registration page.
(iChat Menu > Preferences > Accounts > Press + Button > In the add Pane chose AIM then the Get an iChat Account Button to go to AIM or the @mac.com option and go to the @mac.com registration page).
MobileMe (replaced the .Mac service that original gave @mac.com names) gave out @me.com names.
These will be valid until the end of June in Paid-for accounts.
Along side of this Apple have started iCloud Registrations. These are also @me.com names. However these will not work in iChat 5 or earlier due to the way Apple allows AIM to verify/access the password
AIM valid names can be from AIM themselves, Apple IDs ending in @mac.com and @me.com and possibly some emails of United States ISPs that have similar deals to Apple's with AIM.
You need to supply a secondary email for verification and Password recovery.
That secondary email can be use as many times as you want to create AIM names.
In fact it (the secondary email) CAN BE THE NAME itself (this can be confusing if it is a name that could be valid with another service like a Facebook or Googlemail ID)
This needs and external to Apple email address that is valid. It cannot be an email already used with an Apple ID (as an Apple ID or linked to one)
Keep the password to 16 characters or Less (AIM Server Limit)
I am sure you can find iCloud and register there
Again keep the password to 26 characters or Less.
Rather than have a central server Jabber have loads of servers all over the place.
Your ID is based on a Username part and the Server Name.
Facebook and Google Mail IDs are also Jabber IDs if you enable the Chat or Talk option on your Account setting at either of those services.
Goolge don't stick to the Server name protocol that the rest do and that is why iChat has a separate line for Goolge in the Add account screen
iChat 6 Pic
Uploaded with Skitch!
Facebook can be set up as an ordinary Jabber ID
iChat 6 added Yahoo and you can only use an ID registered at Yahoo (where as the Yahoo for Mac beta can use MSN/Hotmail/Live ID as well)
Please, if posting Logs, do not post any Log info after the line "Binary Images for iChat"
iMac 2.5Ghz 5i 2011 (Lion 10.7.3)
G4/1GhzDual MDD (Leopard 10.5.8)
MacBookPro 2Gb (Snow Leopard 10.6.8)
Mac OS X (10.6.8),
"Limit the Logs to the Bits above Binary Images." No, Seriously