Summer brochures usually launch in May from big operators, with smaller ops following at later date.
EDIT: Just been reading todays Travel Weekly (31/03/06) and there is a full page article about Delta. And I quote
Airline Looks East
UK Regional Airports and eastern European routes are top of Delta Air Lines' wish-list as it plans future services.
The airline aims to launch from Belfast, Glasgow and Newcastle within two years and is considering a Gatwick-Salt Lake City service.
New York back on the cards? Or will CO get in there first?