Your SIM has a UK phone number. Your number will be emailed to you as soon as your SIM is active.
Callers from the UK simply dial your number in local format, for example 07XXX XXXXXX.
Callers from outside the UK simply prefix your number with the appropriate international dial out code.
For example, callers from most European countries dial 00 44 7XXX XXXXXX; callers from the USA dial 011 44 7XXX XXXXXX; callers from Australia dial 0011 44 7XXX XXXXXX..