The more you depend on your iPhone, the more you would need to bring it along for your next overseas business trip. However, if you bought your iPhone on a contract, things might not be so simple. The device will be locked to the network of your telecommunications carrier. You will not be able to use a prepaid SIM bought from a local mobile carrier when you arrive at your destination.

This would give you no other option but to pay your carrier's international roaming rates to while you're overseas. The solution seems simple, get your iPhone 4 unlocked so that it will accept any SIM card or microSIM card you want to use.

Telstra, the telecommunications company, is the only one charging to unlock the device, which would cause about a $150. Its rivals, Optus, Vodafone and 3, will all unlock iPhone 4s free of charge.

If you do manage to get your SIM and number activated while you're overseas, using data may be too expensive unless you find a free Wi-Fi hot spot.

Going online through your phone may cost a fortune in data-roaming charges. Many people get home with a bill for hundreds of dollars in accidental data-roaming fees waiting for them. If you want to use iPhone data in another country, ask about global data-roaming packages.

Vodafone, for example, offers a Roaming Data Bundle that provides 25MB of data for $49. This price comes to about an 80 per cent discount off regular roaming data rates. The usual rate comes to about $10 a megabyte.