Voice-to-text on keyboard in HTC Sense
Go to Settings, Language and Keyboard and see if there is another keyboard you can enable and use. If there is one, check the box to enable it. Then go out and open something that requires text input like an text message. Long click on the text field and choose Input Method. Then change to the keyboard you just enabled. See if it has the microphone.

If you only have one keyboard to enable you could try a third party one like Swiftkey Beta. I use it and it has a microphone option for speech input. Plus the keyboard rocks with all kinds of great features.