UPDATE:Added BT statement. At least one ISP, MetroNet, has felt left out in the cold by BT after the operator rejected its application to join the 8Mbps ADSL trials.
Despite owning their on BT Centrals, MetroNet was rejected due to not having "enough customers across the very limited 21 trial exchanges", said Paresh Morjaria, General Manager, MetroNet.
Admittedly the trial is a tiny one and it may be unrealistic to expect that all providers can take part, although BT has issued very little clear information on requirements.
Typically a handful of other providers have also announced their intention to take part, yet without checking first, some may ultimately be unable to do so.
BT has issued the following statement to help clarify: "BT Wholesale has invited every ISP with customers within range of the selected DSLAM to take part in the ADSL Max trials. We have 28 ISPs listed as potential trialists, some of which only have one single circuit on the DSLAM."