Having the same issue. I compiled a list of notes that I plan on showing today. I thought nothing of it thinking it was network. Stuff happens. I will post back and let you guys know the outcome. Here is my notes for your benefit. It does seem like if the phone is in standby longer the liklihood of the problem reoccuring is greater. I personally think it is a sensor glitch as my raise to speak also doesn't always work right. Otherwise awesome phone. I work in IT and generally find notes as a helpful way for me to wrap my brain around problems. I definitely am starting to think it is a sensor glitch.
1. Problem since day 1 but never thought anything of it. Thought it was network.
a. If I had known I would of had this phone back to you guys on day 1. However I was in a location with low network reception at the time.
2. Probability of the problem reoccurring is greater when the phone is in standby longer.
3. It is almost like the speaker is not turning on or getting power like it is still asleep.
3. Turning off bluetooth sometimes triggers it after a long sleep.'
4. Incoming calls always work properly without a hitch. I think this wakes up the ear piece.
5. No clue if this is software or hardware.
6. Seems like thousands of others are having this problem. The description is exactly what I am experiencing.
https://discussions.apple.com/thread/3404857?start=495&tstart=0
a. US
b. Canada
c. Europe
7. Willing to wait it out for a software update but no clue since some people say a phone replacement solved it.
8. Turning mute on and off always fixes it or speaker on and off.
9. The problem is gradually getting even worse. Fresh iPhone as I have never owned an iPhone before. Restore doesn't work.
10. Mixed reports about Apple knowing about the issue and it is software. Some Apple Stores are just giving out replacement phones which also doesn't always work.
11. Not good for my job as I keep saying hello and can not hear anybody.
12. Timer keeps ticking no audio.
13. https://www.facebook.com/iPhone4SOutgoingCallNoAudio?sk=wall&filter=1 Consensus is that a hardware replacement fixes it.
14. Put phone to sleep for 45 minutes. Made a call to my work phone at my desk. I could hear my work phone but no audio in my iPhone.
15. Totally out of my 30 day window as I ignored the issue but now it keeps getting worse. Wouldn't trade this in for a different phone but want a replacement as this seems to be the only way most individuals are getting the fix.