Just in case you hadn't noticed, Sling have updated the iPhone Slingplayer in the AppStore to V2.4.6. But in accordance with what seems Company Policy as regards updates, they have made sure they have degraded it and removed some functionality. In this case it is the ability to run on iOS lower than 4.3, and the iPhone 3G is, of course, stuck on 4.2.1.
So if you have to send the phone in for repair or it gets a hard reset then you will NOT be able to re-install Slingplayer from the store. The only option is to do a System Restore from within iTunes (right-click on the iPhone icon). So I know you all do it anyway but make sure you always have a current backup in iTunes.
Sometimes (no actually, always) I just despair of Sling Media, they just don't seem to think these through.