A word of warning:
If you’re with 3 Hong Kong (who laughingly call themselves a communications company) and you go abroad, do not send ANY messages, iMessages, SMS or anything else unless you’re on Aeroplane Mode and you’re using LOCAL wi-fi.
This might seem like common sense to the normal person. I do it every time. However, after visiting the UK recently on something of short notice, and not being able to actually find wi-fi everywhere in the UK, I sent a few international SMS. International in that they were sent using my HK mobile number, bounced around the UK, and delivered by whatever local service as needed. Unavoidable.
Then I get the bill. Charging HK$2 for each international SMS is pretty reasonable, but when they charge an EXTRA HK$3.55 PER MESSAGE ON TOP, I get a bit annoyed. Especially as it turned my $300 phone bill into a $950 phone bill.
Add to that the five days it’s taken to actually get hold of anyone at 3 to ask what in the present continuous bloody hell is going on, and you get one very steamed customer.
Moral of the story? Buy a locally-charged SIM card (that fits your phone’s SIM card slot). Or just leave your phone on aeroplane no matter what.