I use Advanced Task Killer ( Advanced Task Killer Android App Review by AndroidTapp.com | Android Tapp. Android App Reviews
) for closing apps and freeing up memory. I have it so that every hour it closes everything other than what i've told it not to.
As for sound ... i think the mp3 sound is about as good as iPod Touch but i don't think the call sound quality is anything special. Before this phone i used a Blackberry Bold and the call sound quality on that was unreal and better (clearer and louder) than any phone i've ever had before.
Still, it's good enough.