General phone numbers have 01, 02 or 03 prefixes, for example 020 8594 0000 or 01332 999 999. 

London numbers all start with 020 and the local number is 8 digits long. Generally speaking, central London numbers will start with a 7, outer London numbers will start with an 8; however, this is not always the case, and there are new numbers starting with a 3.  The first part of the number, which is specific to one town or city, may be referred to as the STD (Subscriber Trunk Dialling) code.  If you are making a local call within one area, you do not need to dial the STD code.  However, it does not matter if you do.

Landlines all start with 01 or 02. Most are 11 digits long. A few are still 10 digits.

Numbers beginning 03 are charged to the consumer at the same rate as calling a geographic number. However, 03 numbers are not yet that common.

Numbers beginning 07 are either mobile phones or personalised numbers.  It is proposed to change personalised numbers to begin 06.

0845.... and 0870.... numbers are similar to 1-900 numbers in the States (pay per call). 0845 numbers are charged at 'local rate' and 0870 numbers at 'national rate' . In the weekday daytime national rate from a BT  residential line is just over 7.5p per minute, local rate 3p per minute.  It is less in the evenings and they  fall to 1.50 and 1p respectively at weekends.

0808.. 0800....& 0500 numbers are the only free numbers when dialled from a landline. Some mobile phone providers still charge for calls to these numbers, so be wary.

09.... numbers are premium rate phone lines and can cost anything up to £1.50 per minute to call. By law, the cost must be advertised. 0901... numbers have a fixed charge - no matter how long you are on the phone, you will only pay the amount stated. 0906 and 0908 ... numbers are charged per minute.  0908 and 0909 ... numbers are for adult services. Mobile phone providers usually bar access to premium rate services as standard.

Numbers which begin with 118 are Directory Enquiry services and are special rate numbers. There is a one-off fee per call, usually in region of 50p. The operator will ask if you wish to put be through to the number you require. By doing this a per minute charge will be added, making it an expensive call. You can say "no", hang up, and redial the number at a much cheaper rate.

To get the operator, just dial 100. For international assistance, it's 155.

Phoning from a hotel can be expensive, as they can charge more than the standard rate. There is no set cost of phoning from your hotel room, so it is advisable to check the rate before making the call.  

Telephone boxes now permit a national call (anywhere on mainland UK) for up to 15 minutes for 30p. Details are given inside the telephone booth.  Note that the price will rise to 40p for 20 minutes as of November.  Most British people have given up using payphones now, preferring their mobiles. But they still have their place, for those times when you're caught short without a working mobile phone. 

For a visitor from overseas, one big advantage of a payphone is that it's generally cheaper than a mobile for international calls.  Payhones are unfortunately a traditional target for vandals and anti-social behaviour, so you'll find that many are dirty and smelly inside, and they may not work at all.

If you're planning to spend a while in the UK, it's worth getting a local SIM card. The UK's mobile industry is fiercely competitive and SIM cards are often given away or sold for £5, which can include credit. This will definitely reduce your bills for phoning home from a mobile phone. Carphone Warehouse also offers a Mobile World SIM which is free when you put £10 credit onto it and offers very cheap calls to the USA and other locations.  Be aware that American, Canadian, and Latin American visitors may need to check with their phone's manufacturer or provider if it will work in the UK.  Lebara is also another carrier offering low rates. In fact, it is only 4 pence to call from the UK to the US or Canada. Cellular Abroad - www.cellularabroad.com - in the offers this SIM card as does Amazon. While it is more expensive to purchase it here than it is in the UK, it is certainly more convenient to have the number as well as the physical product with you prior to your trip.

Other option is to rent a cell phone before your departure, with a local line from the UK, you'll have the benefit of low calling rates, including incoming calls free of charge. You'll find several companies offering this kind of service, be aware of those that use call back since the voice quality is very poor.  Some good options are www.cellularabroad.com,  http://www.phonerentalusa.com/, www.worldcell.com and www.planetfone.com However, cell phones are now so cheap to buy (from about £15 for a basic one) that renting may not be economic. However, these phones are only good for use in the UK as they are locked. You will pay more for an unlocked phone. A locked phone is one that only works with a specific carrier. You can hand the used phone into almost any charity shop where it will be refurbished or recycled and raise money for the charity.

Phone cards are also offered or given away outside many Tube stations, though be sure to read all the small print. It's usually better value to go and buy a BT phone card from a newsagents - they may not be the best value available, but you certainly won't get ripped off.The Post Office phonecard is usually reasonably good value. If you make a call with a phonecard from a public payphone your phonecard credit may run out faster than you expect: there is a 37p/minute levy to support the public payphone network.

The UK's emergency numbers are 999 & 112 for fire, police, ambulance, coastguard and mountain rescue. The operator will ask you what service you need then put you through. Calls to both of these numbers are completely free.

To dial out of to another country from the UK, first dial 00, then the country code + number.

When calling from abroad to the UK, you first dial your international access code.  This varies depending which country you are in.  For example, it's 011 in Canada, 0011 in Australia and 001 in Singapore.  Then dial the country code for the UK (44) and the UK phone number, leaving out the zero at the start.  

Override Providers

One of the cheapest ways to make calls, from any land-line telephone, is to use the override providers,  You dial a special phone number (usually 0845 something) depending on the country you want to call.  Then after a brief intro message (10 seconds or so) you dial the number you want starting with 00 and press the # key at the end and they connect you.  The fee is simply put onto the phone bill.  They charge typically only 1p or 2p a minute to the USA and offer cheap calls to many destinations.  A well-known one is Phonecheap.  

00 is the International Access Code to dial out from within the UK, the Republic of Ireland and all other EU countries. 

44 is the Country Code for the UK.

353 is the Country Code for the Republic of Ireland.