When a call is in progress, use the buttons onscreen to mute or unmute the microphone or to turn the speakerphone on or off. You can also press MENU and choose other options such as muting the microphone, and more.
To turn the speakerphone off, just flip HTC Rhyme over again, facing it up. Or tap again.
If the phone number of the person who called is not in your contacts list, you can choose to save the number to your contacts list after you hang up.