EXPRESS PHONE SERVICE is now being offered by AT&T for US travelers abroad. Through USADirect Service, callers can overcome delays, language barriers, and costly telephone surcharges. For a free plastic wallet card or passport-size sticker listing USADirect information, call AT&T in the United States at 800-874-4000, ext. 333. AMERICANS WILL TAKE MORE VACATIONS this year than in 1987, reports American Express 1988 National Travel Forecast. Despite the stock-market crash - or maybe because of it - almost two-thirds of those surveyed are willing to cut back on luxuries in order to finance more vacation trips in 1988. This trend was particularly strong among Americans aged 18 to 34. VIRGIN ATLANTIC AIRWAYSoffers bargain fares to London from Newark, N.J., and Miami, including a one-way fare of $88, available through Feb. 21. Seats can be reserved one day before the date of travel. Tickets are nonrefundable, however. For the return trip, a $179 Latesaver fare is offered, producing a round trip cost of $267. The Latesaver must be booked within seven days of the flight. GREECE IS MAKING TOURISM a top priority with the establishment of a new Cabinet position, deputy minister of the national economy for tourism. The government has named Nikos V. Skoulas to the post. Two committees have been formed to expedite solutions to any tourist problems and to initiate new legislation to improve Greece's tourism infrastructure.