In GSM there is a standrad GSM code for withholding numbers.. look for GSM codes online.. Many phones have a built in number privacy feature but the Thai networks do not always tend to get it right..
Its rare I see a UK tel number come up even when I am called from the UK landlines or mobiles these days.. Telcos are all using cheap routing systems and they lose the numbers more often than not.
Not safe enough for phoning the wife while at a conference though
