How do I prevent AIM from logging me out?

[SilverK20A3]

Hi! Just got the new Hero on Sprint. I was wondering how to keep the native AIM application permanently logged in? I assumed as long as the lil AIM guy was in my notification bar, I was logged in. However, occasionally, when I click on the IM shortcut, I have to log in again, which means Android logged me out.

PS-The last IM app I actually bought was BeeJive for Blackberry years ago. What's the best AIM app on the Android market? I'm fine with the native app for now.

Thanks!