How to create custom ringtones for iphone 3GS?

I tried the same procedure that's used for iphone 3g. encode file to AAC, rename to .m4r. And it's just 11 seconds. The ringtone even shows up in my iphone ringtones section in itunes! But after syncing it, it just does not show up on my phone. There's no custom ringtone section created. It's frustrating! Is there a different procedure for 3GS?