When using your mobile telephone abroad you really have two choices – one is to use your existing SIM card, if your service provider has a roaming service and you have roaming enabled. The other option is to purchase a local pay as you go SIM card which will give you a local number and you will pay local rates.
The major disadvantage to roaming is the high costs of calling people and of course for people to call you. Let’s say for example that you are in Singapore on business but your appointment at 11am wants to change the time of the meeting he would have to call your number internationally, so if you are from the UK, he would have to call the UK and pay for that call and you would have to pay for the part of the call from the UK to Singapore. A very expensive mess!
This is why the easiest and cheapest option is to buy a local pay as you go SIM card. In doing so if the above mentioned appointment wants to change the time of the meeting all he has to do is call a local Singapore number and you pay nothing. Plus any outgoing calls you make are at good local prices so you are not being ripped off from that angle either.