[UndeadSquirrel]

I read on the T-Mobile forums about a guy whose MyTouch started acting up like mine, and he had an interesting idea about why, and a solution:

A few weeks back I tried to make a call on my phone and I wanted to use the speaker, when I brought up the menu to select "speaker", I noticed that the option was greyed out and so I couldn't enable it. After that I looked at the screen and it said it was dialing, but I heard no sound coming out. Next I clicked the volume control all the way down to mute and then all the way to max volume, still no sound. After ending the call I double-checked to make sure I wasn't connected to any bluetooth device, bluetooth was disabled. So then I tried to change the ringer volume and the speaker emitted its beeps letting me know how loud the ring volume was. That told me the speakers worked as well as the hardware responsible for generating sound. My next idea was to see if the media player had sound, so I played an mp3 from my sd card, no sound, went to youtube and played a few different videos, no sound. Called my friend, who was standing next to me, and when he answered he said he couldn't hear me speaking, I couldn't hear him either.

Something was seriously wrong with my phone so I bit the bullet and reset it to factory settings, the problem persisted. I took the phone to a TMobile store and they got me a replacement phone. The phone was working for 3 days and then the same problem occured. I got another phone (my 3rd phone) and this morning it has stopped working in the exact same way. I don't do any hacks or developer apps. There is no pattern to this except that it always seems like I'm at work when it happens.

UPDATE WITH SOLUTION: After thinking about this issue it occurred to me that the phone was behaving as if it had a bluetooth device connected to it. As an experiment, I went to my car which is paired with my phone and selected the audio source as my phone. At first it couldn't connect to my phone. So I looked at my phone's bluetooth setting and the status for my car's connection was "paired and not connected". I selected the connection on phone and retried with my car and bam, audio now works. I disconnected the phone from the bluetooth and sound was restored! So mytouch 3g has a bug in their bluetooth services. TMobile/HTC, hit me up if you are looking for a top-notch developer to fix your defects.

Unfortunately, this didn't work for me, though it sounded like the BT is the culprit.