The last couple times I was on the phone, perhaps I hit the speaker button on the screen, and then I couldn't get the phone-screen back so I could un-speaker-phone-it.
To get back to the phone screen from another screen just click the BlackBerry (menu) button on the bottom and it will bring up your options....one of which is return to phone.
From there you can just click the normal button to turn on/off the speaker phone.
