What is the correct way to dial a UK 033 number from Thailand using True?

and 006 are the two international dialing prefixes for True. is cheaper, and 006 is supposedly premium quality connections. You dial that prefix, then the country code and number. Of course, you always drop the leading 0 in the phone number whenever you dial internationally, just like you would for Thai phone numbers. So to dial the UK, you would dial -44-33etc, since the UK country code is 44, and you said the number starts with 33 (dropping the leading zero).

Probably 0044 and then drop the 0 on 033