Sprint/Nextel has really fumbled the ball with the 8350i echo problem. They claim that a small subset of users are experiencing an echo issue but by the amount of email I get about it this has to be a very vocal subset. Sprint’s response so far is that they have identified the issue and it will be fixed in March. Their laughable workaround solution tells you to use the speakerphone or headset to avoid the blast.
A creative 8350i user who was not interested in waiting until March found a way to create a hybrid OS out of the TELUS 8350i OS and fix the bug completely. The instructions may be a bit lengthy but they have done a great job of laying them out with screenshots.
Check out the details at this link and let me know if it works for you!