I think it's that same 20 buck phone but in the other post you added to it was not clear it was the same exact phone.
As reports mount you can see the issue. It's broke and given the low cost of the phone my bet is no fix is available. Why not return it as defective?
And no one minds you add to an existing discussion at all. Just add that you have which model and more. It's nice to see the details so you can add it to the pile of what does not work.
Bob
I have a Samsung SCH-S380C. When I receive a text message, I get a visual notification, in the form of a little white envelope in the top portion of the home screen. However, no sound is played.
This question was brought up in a different thread in January but no helpful information was produced so maybe we can try again.
I have been through every. single. menu. in. the. phone. And tried every single setting that could possibly have anything to do with text message alert sounds.
I have used the stock sounds that came with the phone, and I have also used my own sounds that I put on an SD card.
The sound works on my phone, because when I recieve a phone call, it rings just fine. The only problem is the text messages. There is no sound.

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic