iPhone 4 earpiece stops working My wife's iPhone 4 (Verizon) earpiece stops working every now and then.  She has to switch to speaker mode during calls.  

To fix this, she plugs in the headphone and unplugs it.  Not a bad workaround IMO, but very annoying to her.  She's debating selling it on ebay and getting a different phone.

I'm not sure if this is hardware or software related.  Any advice?  Upgrade the software?  Not sure if it will fix it, but we probably will anyway.
This can happen when the contact spring inside the headset jack is loose, cracked or broken, or maybe the plug or jack is just dirty and shorted out.  Perhaps try cleaning/degreasing the plug and then blowing out the jack with compressed air.  If that doesn't work, a visit to the Apple store is in order.

This same problem can happen on different models of other phones as well, any phone that has a headset jack.