Most people use a telephone modem to connect to the Internet. The connection is fairly slow (maximum 57 Kbps), so if you pay for the connecting telephone calls, it can get expensive. A number of ISPs offer a flat-rate service, where you pay them a monthly fee and get the calls for free. This is often called an unmetered service. In the UK, there are hundreds of ISPs with all sorts of tarrifs. Freeserve, BT and NTL all offer unmetered internet services and the cable operator Telewest offers one to customers who take its telephone service. It's hard to keep up with this market. Internet magazine provides a good guide.
Many people find it unacceptable to tie up their phone line for hours while they are on the internet, so they get a second line. This means paying more line rental, of course. If the cable TV service passes your house, it may be cheaper to get the second line from them than from BT, or you could use a cable modem (see next section).
Once you have an unmetered internet connection, you can access much more material than you would be prepared to when you effectively pay by the minute. It's much more feasible to download software, music and video. You can also listen to internet radio radio stations. These "broadcast" a continuous stream of music across the internet.
If you have a microphone and sound card, you can use the services like the MicroSoft Network (MSN) to make phone calls using voice over IP (VOIP). If you have a webcam, you can also make video phone calls. This is called video conferencing, although with a telephone modem connection your conference is limited to two people. Video conferencing is often used by people working from home to call their colleagues in the office. You can use it call your friends too, assuming that they have suitable equipment and they are sitting at their computer, logged into whichever service you are using to call them.
If you do use MSN to make business calls, you have to accept its limitations: it's a free service and offers no quality guarantees. The service may not even be there when you want it. Also, the terms of the service forbid business use, so you depend on MicroSoft not noticing. There are lots of services that support business video conferencing, but you have to pay for them.
Cable modems provide fast cheap internet access over the same connection used to deliver cable TV. The service is unmetered and "always on", which means that whenever your cable modem is switched on, your network is connected to the internet. The service does not use the telephone line, so that is free for voice calls.
The service is restricted to streets which are covered by the cable service. In fact, incompatibilities within the networks restrict that further - even if you can receive cable TV at your premises, you may not be able to use a cable modem.
NTL and Telewest both offer cable mode services aimed at homes and small businesses.
You can only use NTL's domestic cable modem service if you also take one of their telephone lines. Many people take the extra line, transfer their number to it and give up their BT line. (I would advise doing that in stages. Don't cancel your BT line until you know you are happy with the NTL line.) The rental is comparable with BT, but the installation is cheaper. The call tarrif is different, so your calls may be cheaper. You get the basic TV service for free with the phone rental.
The 64 Kbps cable modem connection is comparable in price and performance to an unmetered telephone internet connection.
The 500 Kbps connection costs £20 per month, plus the rental for the mandatory telephone line. If you give up your BT line, you can ignore the line rental, because you were paying that anyway.
Those prices assume that you buy your own cable modem, which I did. It costs about £180. You can rent one from NTL for an extra £5 per month, so buying one pays for itself in about eighteen months. If you buy, you are responsible for getting it fixed if it breaks, of course, but they seem pretty robust. You have to buy the modem mail order from NTL's approved supplier. They will advise you.
NTL's cable TV service is digital. They also run an old analogue service with less channels for existing customers who haven't upgraded. Both services support cable modems, but they use different modems. If you take the old analogue service, you have to specify this when you buy your modem. (With an eye to the future, it may be a good idea to switch to the digital service before you buy the cable modem. I presume that NTL will withdraw the analogue service eventually.)
The high-speed connection allows much faster web browsing and downloads. It supports streamed audio much better and allows higher-quality video.
Telewest offer a similar range of services to NTL, but there are differences. For example, they don't bundle their services together, so you can get just a cable modem connection from them without taking their telephone line. On the other hand, they don't let you buy your own cable modem, you have to rent one from them.
Domestic cable modem connections provide only a dynamic IP address, granted on a lease. This means that your IP address is subject to change every few hours. This and other measures prevent you from running your own public web server at home. Your web pages are stored on NTL's web server. (You can build a web server at home and connect it across your LAN, but your friends cannot connect to it, so it's only useful for testing.)
A group of cable modem customers share a connection to the rest of the network. This can cause contention when too many people try to use it at once. Everybody gets a share of the connection, but you don't get the whole benefit of your fast modem. The number of people on each of these shared connections is called the contention ratio. The higher the ratio, the more chance of contention slowing you down.
The more expensive business-class cable modem connections run faster (various speeds) and have a lower contention ratio. The NTL package includes rental of a modem and a gateway. These connections offer a set of fixed IP addresses, so you can run your own public servers, as long as the traffic is not too heavy.
The connections are asymetric, meaning that the data flows faster into your premises than out of it. For example, 500 Kbps incoming and 128 Kbps outgoing. This is OK for a domestic connection, because you never send out much data. It's not so good for a small company running a web server. Your business-class cable modem may offer 1Mbps incoming, but only 256 Kbps outgoing. The incoming speed determines what performance your staff get when they access somebody else's web server, but the slower outgoing speed determines the performance that your customers get from your web server.
The interface to the cable modem can via the Universal Serial Bus (USB) or ethernet. It's your choice, but you have to specify which when you order the modem. For flexibility, choose ethernet.
As with cable modems, the service is restricted geographically, this time because of limits on cable length. You have to be within a couple of kilometers of your local BT exchange. You can find out from the BT Intenet site whether or not you can take the service at your premises.
There is similar set of choices as with cable modem connections: speed; contention ratio; style of interface (USB or ethernet) and price. The incoming and outgoing speeds are asymetric, as the name implies. The cheaper connections were all USB only, but that may no longer be true.