iPhone speaker stopped working.

Does your iPhone speaker no longer work but your headphones do? This is a pretty common issue. Your phone is probably not damaged.

Usually it’s caused by the headphone jack sensor being stuck perhaps due to some dirt or dust on the sensor. Here is how you can fix it. Just play some music or something and insert the headphones in and out several times. This solves it almost every time.
If this won’t work, you can try something more drastic to actually clean the sensor. See the video here.

Headphones and Speakers do not work. No sound at all:

This problem is usually software based - meaning in the OS. You can do the following things (in this order) to try to fix it. Each step is more drastic than the previous so hopefully the first one fixes it, if not the second:

• Reboot the phone. Hold power, slide to power off, power back on.
• Reset all settings. This step is less drastic than the next, but you wil lose some settings. Load settings, general, reset, and click “Reset All Settings”.
• Restore - If the reset did not work, you can try to restore and jailbreak again.