Turkish Lira (TL). One Lira is approximately 40p. It is better to exchange money before you go to get more preferential rates although ATMs and exchange services are available in cities and towns, normally for a small charge.
Turkish, although English or German are also widely spoken, particularly in the tourist areas along the Aegean Coast.
+90 for Turkey then city codes are three digits such as Ankara 312 and Istanbul 216 (Anatolia) 212 (Thrace)
UK passport holders do need a visa to enter Turkey. You can obtain this from the consulate in advance, but in most cases it is easier and cheaper to purchase a tourist visa on arrival in Turkey. You will need to have a valid passport for the duration of their stay to enter Turkey, proof of departure plus proof of sufficient funds for their trip. Note that UK citizens must pay for their visa in £ - currently they cost £10 so be sure to keep some sterling on you.Current Foreign Office Advice for Turkey