How to sms back to Singapore from China?

My mum has her office in china...so I kinda go back quite often to visit...
So if i were there and I needa send anything back to my friends in singapore...the only thing you needa do is to add a +65 to the number given...
for example you have a singapore number of 91234567
The only thing you needa fill for the sent number box is +6591234567
Hope it helps...=]