For True,
*****
is the prefix code for the cheapest rates, or 006 is the prefix code for still-discounted but higher rates and supposedly is a "premium" quality connection. Last I checked, calls to UK using 006 is 5 baht a minute for fixed lines, 7 baht a minute for mobile numbers and using
*****
is 2 baht a minute for either type of number. You just dial
*****
(or 006) 44 etc. to call the UK. No + symbol should be used. By the way, AIS & Dtac have the same type of prefix. For AIS, it is
*****
and 005, and Dtac is
*****
and 004.