It's a fairly common problem: you plug in headphones to your iPhone (or in my case, it was an iPod Touch) and the speaker works just fine for alerts and phone calls, but pull out the headphone cable and the device won't play through the speaker at all. The fix is actually surprisingly simple: just grab a cotton swab, pull off some of the cotton, and get up in there.
Saw Tun explains the issue in the video above, and how he went about fixing the issue. The real problem is that some debris or moisture has shorted out the contact that switches from headphones to speaker inside the headphone jack—not that the speaker itself is busted. Cleaning it out with a swab is a quick fix to what could be an expensive repair if you left it to Apple. We're willing to bet the same issue happens with some Android phones too, so it's worth keeping in mind even if you don't have an iPhone or iPod Touch.
How to fix the iPhone speaker problem (water damage) | The Blog of Saw Tun via Boing Boing