Unlike with some other smartphones, you must first wait until your call goes through turn the speakerphone on or off with the Sprint Mogul by HTC—a Windows Mobile 6 Professional (formally called Pocket PC Phone) device.
After the call goes through, tap Menu and select Turn Speakerphone On or press and hold the Talk button (the one at the base of your handset with the green light-up phone) until the speakerphone turns on.
When speakerphone is activated, a phone icon appears in the title bar. To turn the speakerphone off, tap Menu and choose Turn Speakerphone Off, or hold the Talk key again until it turns off. (Tapping the onscreen Talk key will not activate or de-activate the speakerphone.)