My Verizon iPhone 4 32GB earpiece speaker quit working too a couple days ago 😡 I tried the rebooting and the headphone jack trick, no luck. I took it to Verizon, and as they don't touch apple products - they overnighted me a brand new iPhone 4 🙂
I never have spilled any liquids on it, so that is ruled out. I did drop it about 6 inches onto my end table the night prior after fumbling in the dark to re-dock it in my alarm clock. Maybe that did it, but if that is the case, I am truly disappointed in the craftsmanship/durability of its internal components. I did much worse to my AT&T iPhone 4 and never had any problems.