Don't forget this:
http://www.clickz.com/showPage.html?page=3629297
For the upcoming trial Adam Liversage, BT's chief press officer said:
"We won't know who any of the users are, so any feedback we receive is likely to be the customers choosing to do so through our forums,"
Note, this means anyone in or out of the trial can post feedback in the forums and BT can't distinguish.