There may be times when you WANT caller ID to be displayed to the callee, with your Google Voice number.
In those cases, you have two options:
1 - Call your Google Voice number, hit *, enter your PIN, then choose 2 and dial the number you want to call.
2 - While logged into GV, click the call button. Enter the phone number to be called. It will ask you to choose the phone you want to use (e.g., work, home, cell, etc.). When you answer your phone, the call will be put through to the callee.
I rarely have to do this, but when I call someone who won't answer without caller ID, this works well.