I have a 650. I like it a lot except for one big annoyance: When entering a PIN or similar response (example: voicemail), the first digit is often ignored. I don't hear the keyboard beep on the first digit pressed. If I press the first digit again, then the remaining digits, it works.

Example:
PIN = 12345
I often have to press 112345 to get the 5 digits to actually take effect. The keyboard beeps begin with the second digit pressed.

This behavior is identical on two 650s I have used. The first was replaced for a defective headphone jack. The 650 behaves as if it is not ready for keyboard input all the time.