The old checklist used to be PMT - passport, money, tickets. Then it was extended to include credit cards and cameras. And now, in the last couple of years, the mobile phone has also appeared on the "never travel without" list. It seems to have become essential, even on holiday, to keep in touch with family, friends, even work colleagues, or simply to gossip so we know what's happening at home. And when those airport delays kick in, what better way to moan than down the mobile to a mate.

Since the mobile has become such an integral part of our lives it is natural to assume it will operate effortlessly whenever and wherever we wander the world. However, that's not altogether true. There's a minefield of tariffs, technology and terminology to wade through before you can hook up globally. But they are hard to beat for convenience and still cheaper to use abroad than hotel or pay phones.

Bands on the run

Here comes the technology bit... Most of the 45m mobile phones used in the UK are dual band - that is, they are designed to operate on the GSM 900 (Global Standard for Mobile Communication) and GSM 1800 frequencies used by networks in the UK and Europe.

However, to make life interesting, there is a third GSM frequency - GSM 1900 - that is used across North America and Canada. So, if your mobile is only dual band, it won't work there. You'll need to dig deep and invest in a tri-band mobile to make and receive calls and text messages from the other side of the pond.

The importance of networking

The networks - Virgin, Orange, Vodafone, One2One and BT Cellnet - all charge different rates for "roaming", which is the technical term for using your mobile abroad to make and receive calls and messages, as they have negotiated different deals to use the various foreign networks.

Some of the UK networks initially "lock" phones to UK-use only when you first sign up - unless instructed otherwise. You therefore have to specify if you want to use the phone abroad in order to get the network to activate roaming. Be warned: some networks can take as long as 14 days - the time you may spend away - so plan ahead or it might be quicker to send a postcard.

It costs to talk (and text)... the double whammy

In the UK when you use your mobile, you pay only for the calls and text you send. Travel beyond these shores and you'll pay to receive calls and text, too. This can make your bargain break a very expensive affair as you may be racking up charges you are unaware of. Rates vary from country to country as well as across the networks.

Popular pre-pay

Pre-pay is proving to be hugely popular - with its freedom from monthly bills and binding contracts. But until recently, pay-as-you-go users were the poor relations of the chattering classes, with contract users getting more choice from the networks. However, now that two-thirds of mobile users are pre-pay, some of the networks have responded by including roaming abroad. Coverage and charges vary.

The big pickup: voicemail

It can be frustrating leaving frantic messages on a friend's voicemail in France, only to discover that they found them impossible to access. Unfortunately, this is fairly typical because the retrieval system can involve a maze of pin numbers and codes more suited to Mission: Impossible than a mobile. It's worth getting familiar with the retrieval system before leaving the UK, and remember to keep voicemail messages short - it's an expensive way to learn how boring the office is without you.

Out on a SIM

The SIM (Subscriber Identity Module) card is your phone's fingerprint, and it's specific to you. It's smart and allows you to access the network, receive calls and store all those embarrassing pet names for people. About the size of a stamp, the SIM card goes with you when you upgrade to a new phone.

But it is now possible to buy a pre-pay SIM at many holiday destinations or international airports to make your phone work while you're away and avoid all those hefty and confusing charges. You just remove and store the UK SIM and replace it with the new one for the duration of the holiday.

Charge of the travel-light brigade

In a world of miniaturisation, the charger is a giant bit of kit to cart around. And that's before you wrestle with the adaptor and plug in your hotel room. The solution may lie in the disposable charger, the instant answer to a dying battery abroad. Only if you have a Nokia or Motorola phone though. They cost £9.99 (refills £5.99) from the Carphone Warehouse (0800 424800, www.carphonewarehouse.com).

Handsets - the best travelling companions

Dual band:
• Ericsson A2628, £20. Voice-activated dialling and a six-hour battery make this a good-value talker.

• Nokia 8210, £50-£80.

Lightweight, big memory, good value.

Tri-band:
• Motorola Timeport 250, £50-£150. The latest must- have accessory. A phone that is guaranteed to turn heads on the beach.

Travel tips

• Do your homework: check with your network how much it costs to do all the things you take for granted at home - call, text, voicemail - both inbound and outbound, and to both landline and mobile receivers.

• Get roaming activated on your phone well in advance of your departure so you're not locked out by the network when you arrive.

• Don't forget an adaptor for your charger plug.

• Add 0044 to your phone book numbers to make dialling home speedy and easy.

• Make a note of your mobile's serial number and keep it handy. That way, if the phone is stolen you can contact the network to block any calls being made.

Roaming holiday - a rough guide to call charges

Virgin

0845 6000600
www.virgin.com/mobile

America
From UK to US: 20p per min.
From US to UK: £1 per min.
Text to UK from US: 30p flat rate.
Receiving text from US: free.
Voicemail retrieval: £1 per min.

Europe
From UK to Europe: 40p per min.
From Europe to UK: 65p per min.
Text to UK from Europe: 30p/min.
Receiving text from Europe: free.
Voicemail retrieval from Europe: 55p-65p/min.

Orange

07973 100150
www.orange.co.uk

America
From UK to US: 15p/min.
From US to UK: £1.10/min.
Text to UK from US: between 4p and 7p per text.
Receiving text from US: free.
Voice retrieval from US: 55p/min.

Europe
From UK to Europe: 20p/min.
From Europe to UK: 60p/min.
Text to UK from Europe: 4p-7p/min.
Receiving text from Europe: free.
Voice retrieval from Europe: 30p/min.

Vodafone

07836 191191
www.vodafone.co.uk

America
From UK to US: 17p/min.
From US to UK: £1/min.
Text to UK from US: about 20p.
Receiving text from US: free.
Voice retrieval: £1.15/min.

Europe
From UK to Europe: 30p/min.
From Europe to UK: 60 to 70p/min.
Text to UK from Europe: between 18-30p.
Receiving text from Europe: free.
Voice retrieval: 60 to 70p/min.

BT Cellnet

08705 678678
www.btcellnet.net

America
From UK to US: 59p /min.
From US to UK: 80p/min.
Text to UK from US: 13p - 91p.
Receiving text from US: not available.
Voice retrieval: £1.20 - £1.69/min.

Europe
From UK to Europe: 90p/min.
From Europe to UK: 99p/min.
Text to UK from Europe: from 9p.
Receiving text from Europe: free.
Voice retrieval: about 99p/min.

One 2 One

08454 121121
www.one2one.co.uk

America
From UK to UA: 10p-£1/min.
From US to UK: about 92p /min.
Text to UK from US: 18p-28p.
Receiving text from US: free.
Voice retrieval from US: 92p/min.

Europe
From UK to Europe: 33p-£1.01/min.
From Europe to UK: 70p/min.
Text to UK from Europe: 20-30p.
Receiving text from Europe: free.
Voice retrieval: about 60p/min.

The table above is intended as a general guide to average prices only. There is a world of tariffs and contracts out there - for details, call the individual networks.