AIM users have the ability to configure their account to send messages to their mobile phone when they are offline. When someone does this, their screen name appears to be online 24/7, even when the person is not directly logged on. AIM and other clients I have used will basically show these people as away, with "Mobile" as the away message or something simple like that.
Through the gateway, these users show up as online and available all of the time. It would be nice to be able to distinguish between the two states through the gateway in Spark.