The BBC has confirmed that the Season Four cinema trailer will make its debut on British Television on Saturday 22nd March 2008. As well as being shown on BBC One around 7pm, the preview will be available on the official BBC Website.
With David Tennant and Catherine Tate now confirmed as guests on the BBC1Jonathan Ross show on Friday 4th April, it is looking likely that the series will return to BBC1 on Saturday 5th April 2008.
18th March Update: The new edition of the Radio Times has the trailer listed asDoctor Who Series Four Preview, between the film Toy Story and casting showI'll Do Anything at about 7:05pm.
(note: the BBC website have corrected a previous broadcast date of 29th March as reported yesterday)