Business travellers love that their smartphone keeps email, Web sites, apps and online services just a few taps away.

But as many have accidentally discovered during an overseas trip, the cost of using 3G data as a ‘roaming’ service is a killer.

Use you smartphone overseas and you’ll be slugged an average of $15 per megabyte, which is about 300 times the cost of a domestic data plan – leading to a post-trip bill for hundreds or even thousands of dollars in accidental data roaming fees.

And while tourists can blithely switch off their mobile and rely on email at Net cafes to stay in touch, to most business travellers their smartphone is an essential bit of kit.

It's not just about calls and emails, but those oh-so-handy apps when you're out and about.

Google Maps is a perfect personal navigation system when you're walking around an unfamiliar city.

Airport apps let you check the status of your flight and stay on top of delays and gate changes. Then there are the likes of Urbanspoon for discovering great places to eat and drink.

The problem isn't only that you become so accustomed to tapping an icon to get your information on the go, that you forget the amount of data being sent and sucked down behind the scenes.

Some of this megabyte-munching activity happens in the background and can catch you totally unawares.

A few years ago I visited Beijing with a colleague, and after our three-day business trip he was hit with a data roaming bill for his BlackBerry of over $500.

The reason? His BlackBerry was automatically checking his email account to see if new messages had arrived, and was doping this roughly every 15 minutes.

Each quick email check created a 'data session' with the local Chinese telco, and just that action alone came with a cost – even if there were no emails to download.

So here are three strategies to avoid getting reamed by data roaming on your next trip.

Disable data roaming

If you can make do without data, disable your phone's data roaming feature so it won't consume any data on an overseas network.

This effectively turns your smartphone into a dumbphone which does only voice and SMS.

On the iPhone: open the Settings app and tap General, then Network, and set the Data Roaming switch to 'Off'.

For Android smartphones: click Settings, Wireless controls, Mobile network settings and uncheck the 'Data roaming' box.

For BlackBerry devices: choose Options, Mobile Network, Data Services and select the 'Off When Roaming' setting.

You'll still be able to use your smartphone for Internet and apps when connected to the wifi network in your hotel or any handy cafe.

(This can also be handy to preload the local Google Maps set into your device and then use the app 'offline' as a pocket street map when you're out and about.)

Buy a global roaming pack

If you don't want to forego the benefits of all those apps, and enjoy 'anywhere anytime' access to the Net, add an international data roaming pack from your Aussie carrier onto your existing smartphone.

This gives you a chunk of data to use overseas, provided you're in a country which has a network partner for your Australian telco.

Here are the links to international data roaming options for Telstra, Optus [PDF] and Vodafone.

The prices are still incredibly steep, from $20-$40 (depending on the carrier) for a mere 10-15MB. But they're a fraction of what you'd be hammered for casual data usage if you didn't buy an international data pack or plan in advance.

10-15MB is sufficient for basic email, some very light web browsing and simple app usage, but steer clear of YouTube and other streaming video services.

It's best to overestimate how much data you'll need, and pay a bit more up front, because excess usage can see you slugged at the casual connection rates.

(I'll also share a real-world travel tip. If you prefer to be roused from sleep by your smartphone's alarm rather than rely on a wake-up call from the hotel, set your phone to 'flight mode' before bed. This will stop you being woken at 2am by a call from Australia where it's middle of the afternoon!)

Buy a local data plan

A far more cost-effective option is to swap your Aussie SIM card for a local prepaid voice & data SIM when you arrive at your overseas destination.

You'll get internet access at affordable rates – literally 90% cheaper than global roaming rates – and you'll also be able to make low-rate calls to local numbers rather than be hit for several dollars per minute.

A bit of research online can help find the best deal before you travel, although when setting foot in a new country I sometimes rely on any telco that's set up in the airport.

They might charge me a little more than a downtown shop but I know they'll be used to dealing with travellers and I'll be connected before I even leave the airport.

Alternatively, call ahead to your hotel and ask if the concierge can recommend a local SIM card or even buy it in advance and have it waiting for you on arrival.

Just make sure your smartphone is 'unlocked' from your Australian carrier before you fly, or it won't work with a SIM card bought overseas.

The main drawback of using a local SIM is that you'll no longer be reachable on your regular Australian mobile number.

I suggest changing your voicemail greeting shortly before you fly out of Australia, with the new message asking calls to email you instead (and not to leave you a voicemail, as you probably won't pick those up until you get back home a week later).

Be sure to stow your Aussie SIM card where it won't be lost. I tuck mine into a zippered compartment in my passport wallet, which also contains the iPhone's SIM card removal toothpick so I can easily swap back to my regular SIM card as soon as I'm home.

And hang onto your overseas SIM cards: if you ever visit the same country again you need only pay a small top-op fee to be back online.

What are your strategies to keep from being reamed from roaming fees? And which overseas mobile networks and SIM cards do you recommend?