There are a lot of ways to turn on your speakerphone – some devices have a built in hardware buttons, others require you to turn on the screen and press a button, but the easiest and most universal way to turn on your speakerphone is simply by a long press of the Call Start button while you’re in a call. This works on all Windows Mobile devices (or at least the ones that I have tested). Thanks to sooby for the great tip (from our HTC Touchscreen forum).