The AccountManager and Account interfaces are implemented in Mission Control 5.
Mission Control 4 implements a completely different interface which is not documented here.
The Account Manager is implemented as part of Mission Control and is responsible for keeping a list of accounts (e.g. XMPP/Jabber, IRC, MSN). The Account Manager is also responsible for maintaining the Connection to each account and setting the presence on that connection.
The service is available on the session bus via the well-known bus name org.freedesktop.Telepathy.AccountManager, object /org/freedesktop/Telepathy/AccountManager and interface org.freedesktop.Telepathy.AccountManager.
To get a list of all accounts known to the Account Manager, you can access the ValidAccounts and InvalidAccounts properties, both of which return an array of D-Bus objects. Valid accounts are accounts that are complete and usable for establishing a connection to a remote service. Invalid accounts are incomplete or otherwise unusable and cannot be used to establish a connection.