The advice at Broadbandbuyer.co.uk on the BT iPlate page is:
1) Although 7 out of 10 homes can benefit to some extent, line speed improvements cannot be guaranteed in every case as the level of interference present on different ADSL lines can vary greatly.
2) The instances below indicate where the iPlate will have little or no effect:
- Where there is already an SSFP (Service Specific Front Plate) installed, thus separating the broadband and telephone signals
- Where the socket is a newly installed BT Openreach socket (with BT Openreach Logo)
- Where the line is newly installed, without the bell ringer wire included