As I await my replacement Treo 650, my thoughts return to its echoing problems.

I have now found that if I remove the phone from the Treo leather case, the echoing significantly diminishes. If I plug in the mic/earphone combo and cover the earphone, there is very little discernable echo on the landline side.

Ah ha .. no wonder there is the ubiquitous low volume in the units' earpieces. Somehow audio is being directed from the 650's earpiece to the mic (and this is aided by the leather case acting as a conduit).

So... the sensitivity of the mic should be reduced (I get complaints that I am very loud) and/or the codec tweaked. Perhaps the 1.15 version of the firmware addresses the microphone issue.