None of this is a standard feature on mobile phones in the high street, but even a fairly ordinary mobile can check share prices or football scores, act as an answering machine, or send text messages. More advanced models can connect to a computer to send faxes, or access the Internet. And, as long as it is on a digital network, a mobile phone will also work abroad.
Extras, though, bring extra costs. There is usually no monthly charge for fax and data, but networks can charge around pounds 30 to set them up, and the interface for the computer costs at least pounds 100.
Using a mobile abroad - also known as roaming - again has no monthly charge but subscribers pay to receive calls. This can cost as much as 50p per minute. Networks normally ask for a deposit for new customers who want to make and receive calls overseas. The deposit varies between networks and tariffs, but pounds 250 is common.
Not everyone wants to use a mobile phone with a computer, and there are plenty of people who have no interest in taking a phone on holiday. Even at home, though, there are other "optional" charges.
Most mobile phones are sold with a contract for using the service - the equivalent to renting a BT phone line. The contract sets out the full costs, which do vary. Orange and One 2 One's contracts are with the networks themselves, so the costs are consistent. For Vodafone and Cellnet, most subscribers still sign up with a third-party airtime provider, which sends out the bills, and sets the prices.
Peak hours vary from company to company. A digital (GSM) mobile phone on Vodafone, with an airtime contract with Vodafone Retail, has peak hours of 8am to 8pm, Monday to Friday. Cellnet's recommended peak hours are 7am to 7pm, as they are on Orange and One 2 One.
Insurance is another cost to take into account. The full cost of a mobile phone handset is usually between pounds 200 and pounds 400: the prices in shop windows are only for new subscribers. Lose the phone within the 12-month contract, and you will have to pay the full cost. Some household insurance policies now cover mobile phones, but if not, the network or airtime provider's charges are worth bearing in mind.
One 2 One charges pounds 2.99 a month for insurance. Dial-a-phone, a mail order dealer and airtime provider, charges pounds 13.47 for three months' insurance for a phone on either Cellnet or Vodafone. Orange includes insurance free of charge for the first year.
Insuring a phone is at least optional. Other charges are harder to escape. First, there is a connection charge. The industry's standard charge is now pounds 35, although there are occasional special offers with free connection. Itemised billing is free on Orange and One 2 One, but on Vodafone's price list it is either pounds 1.50 a month, or pounds 2.94, depending on the tariff.
Some airtime providers make itemised billing mandatory, in effect adding as much as pounds 2 a month to the bill. The advertised monthly subscription normally applies only for payment by direct debit. If you want to pay by cheque, this can add almost pounds 3 a month to bills.
Calls that are free from a normal phone can also be expensive on a mobile. Calls to a Freefone 0800 number are charged at "normal cellular rates" on Vodafone and Cellnet, but they are free on Orange and One 2 One. If you need to call directory enquiries, it makes sense to use a phone box. A 30-second call on a Vodafone digital tariff costs 30p. On the older, analogue system the minimum charge is pounds 1.
Answering services are vital to many mobile users but, again, costs vary. Vodafone and Cellnet charge 39p per minute to listen to messages (Vodafone will reduce this slightly in January, 1998). Orange charges 7.5p per minute, excluding VAT, while One 2 One does not charge at all. Calls to the answering services, as well as calls to other mobiles, are excluded from most networks' inclusive "free" minutes.
By keeping an eye on such charges it is possible to run a mobile phone economically. Cellnet claims that 1 million of its customers - a little under half the total - spend pounds 20 a month or less.
Spare a thought, though, for people who have to call you. It is frequently cheaper to call from a mobile phone to a fixed, BT line, than the other way round. On Cable and Wireless's Call UK service, formerly Mercury, it costs 31p per minute to call a Cellnet or Vodafone mobile at peak times, and 27p per minute to call an Orange or One 2 One phone. BT's standard residential service charges 38p per minute to call a Vodafone or Cellnet phone peak rate. Calling Orange and One 2 One is significantly cheaper, at 17p per minute, but this compares with just less than 8p a minute for a peak-rate BT call.
Anyone who uses a mobile phone a lot will find that he or she saves money by signing up to the same network as relatives, friends or colleagues. Calls between mobiles on the same network are the cheapest of all. Orange charges the off-peak rate at all times for Orange to Orange calls; while some Vodafone tariffs charge calls within its network at a cheaper rate.