My Vista 390 Corded phone works fine except for the microphone. When I push the "Speaker" button I can hear the other person fine but they can't hear me. This only happens in my (older) house. I've tested the phone at the store and the microphone works fine. I do have DSL filters on the phone line. Don't know if that's relevant or not.

SOURCE: we have just bought a Vista 390 and are not able

It took me some time, but I found out from the manufacturer Aastra (1-800-288-1683), that the issue with the Vista 390 hands free speaker is related to your internet connection. If your internet is connected to your phone line, you will need to put at least 2 DSL filters on your Vista phone line. I had to put 3 before I could use the speaker phone feature properly. 1 filter by the wall, one by the phone and had to connect a 3rd one before the two-way speaker feature would work properly. Your phone service provider should be able to provide you with these DSL filters...