No one can hear me on any of the handsets - Uniden TRU9585-4 Quad Cordless Phone

To be check handset speakerphone part or electronic part for that speakerphone. There is difference handset speakerphone and speaker.

What model VTech DECT 6.0 phone?

try unpluggjng base unit from power supply and then let handset unit reset to relocate the base unit.

The mic for the handset was not soldered correctly.
After re-soldering it, the handset worked perfect.

SOUNDS TO BE A PROBLEM WITH THE EARPIECE ON THE HANDSET WHICH MEANS THE HANDSET NEEDS TO BE REPLACED.

It sounds like you have a defective handset cord or handset. First, at your phone, switch your handset with another phones handset that you know for sure works. From your phone make a test call. If the caller can now hear you, the original handset from your phone is defective. If the caller still can not hear you, switch your handset cord with another handset cord from another phone that you know works. From your phone make another test call. If the caller can hear you, then your original handset cord is defective. You can purchase another handset cord from your local office supply store. Your phone uses a standard handset cord. It may be difficult to match the original color of your handset cord. Be sure to take your defective handset cord with you, so you can try to match the color. If the caller still does not hear you. Put your original handset and original handset cord back on your phone. Then plug your phone in to another wall jack, that you know works with another phone. The other phone needs to be an identical phone to yours (same number of buttons and same model number. The model number can be found under the phone). Wait approximately 90 seconds, sometimes longer, after you plug your phone into the other wall jack. Now, make another test call from your phone. If the caller can now hear you from your phone with it plugged into another working jack, then you have a defective station port or jack where your phone was originally plugged in at. If the caller still can not hear then you have a defective phone.

These phones are extremely durable. The most likely cause is a bad handset cord, which is a standard modular type and easily replaced, or possibly just a bad handset, which is proprietary. (The handset cord connection at the handset is hidden by a snap on cover you can remove with a small screwdriver or fingernail file. Pry it just above the cord as it enters the main handset body.)

don't hear with uniden 640 dcx

The microphone in handset is broken!

Try Ths on the handset Be sure the TALK indicator is off.Press LOUD/RINGER button on the handset, the curreent ringerwill sound. To change the Volume press the LOUD/RINGERagain within 5 secs , and the new ringer will sound, you must press LOUD/RINGER within 5 secs or the volume will not change.