You mention that adding 141 to the start of the number has worked for you (presumably when overseas, you're dialing +44-141-191-490-7900 or whatever the UK number is now). I imagine that it does work in some places outside of the UK, as might putting #31# in front of the number you want to dial which in the UK usually does the same thing as putting 141 in front. It is such an easy option that it is handy when it works

In my experience, however, I tend to find that dialing 141/#31# doesn't work when in the States/South Korea/Italy using my UK mobile. Presumably because 141 isn't a valid code over there. I just get a "this number has not been recognised" instead and have to take off the 141. Remember, that you'll be dialing 141 to the local network (e.g. AT&T USA) rather than your home network (e.g. Three UK; Vodafone UK, etc). It is more than likely that they don't have the code set up on their network.

If you do want to withhold your number and 141/#31# isn't working then you might be more successful using your network settings to withhold your number (e.g. http://apple.stackexchange.com/quest...h-an-iphone-5s). Again, remembering cmcbugg's advice to re-enable it so your friends don't get PPIssed off.

Even then, I'm under the impression that some overseas mobile networks don't respect the setting to withhold your number (or at least don't handle it in the same way as in done in the UK).

Simon.