Iphone 4 help

I have an iphone 4 with a few issues. One is a deadspot under the crack on the screen, but I can get that fixed simply enough. The backlight also flashes really fast, like between 2 brightness settings, also can be fixed with a new display assembly. I am waiting to do that until I find out if this other issue can be solved. Essentially, it plays no sound during calls. I have tried with regular, headphones, bluetooth, and speaker, still nothing. The weird part is that it plays sound for music, and it will play voicemail over the earpiece (and speaker). This would lead me to believe that it is a software issue, except that I have tried restoring it and updating etc. multiple times. If anyone can give me any help, I would really appreciate it. My only priority is to spend as little as possible, because I am getting a new one in mid/late november.