I found this online:
"If the onscreen keyboard does not display a Microphone key, voice input is not turned on or you have it configured to display on the symbols keyboard. 1 Press Home , press Menu , then touch Settings > Language & keyboard > Android keyboard.
Or you can also touch & hold the Symbol key on the onscreen keyboard; in the dialog that opens, touch Android keyboard settings. Touch Voice input. Touch the option for where you want the Microphone key (on the main keyboard orthe symbols keyboard). Or touch Off to turn off voice input."
For me neither option allows me to access or see the microphone.