Hardly a week goes by without a new voice over IP (VoIP) offering being announced, and if you have a broadband internet connection you can take advantage of these services.

The initial offerings were one-way - you could make calls to conventional telephone numbers but they couldn't call you back. The current crop offers a wide range of phone numbers, typically London numbers or 0870 ones, as well as other local area code numbers, and communications watchdog Ofcom is also offering numbers in the 054 range for users not always at a particular location.

The prices are low but it's not a good idea to use VoIP just to save money because similar tariffs are available for conventional landlines. However, there are many other attractions to the new services, especially for smaller companies. For example, it is easy to set up a Centrex-like service where no private branch exchange (PBX) is needed and each employee has a VoIP phone connected to the office local area network (LAN). This can save a lot of money and, because calls can be redirected to any internet connection, it is very useful for employees on the road.

VoIP services have advantages for the increasingly-popular "distributed company" where employees work from home or are in several small offices. VoIP can make the whole thing look like a conventional structure with all the PBX features and systems that would otherwise be set up with conventional telephone lines, which would be more expensive and not so flexible.

However, not everything is rosy, since the performance of VoIP systems depends on the quality of the internet connection. A few seconds interruption is usually not a problem for a data service but can cause serious difficulties when it comes to voice calls. In addition, you have to think carefully about what happens when the power fails. It is taken for granted that a conventional phone line just keeps on working, but with VoIP, battery-backed systems will be essential and a lot of LAN kit will have to be protected for voice services.

Then there is the issue of 999 calls. A conventional call to the emergency services has higher priority and the networks provide information about the location of the phone, whether fixed or mobile. Providing higher priority on the internet is not a trivial matter, however, and how do you provide location information when the caller could be anywhere in the world? As a result, VoIP network operators are not keen to support 999 calls.

Ofcom has been looking into regulation of VoIP services and has consulted widely. The question of access to the emergency services has been the hottest issue. The conclusions should be available soon, although Ofcom has already indicated that it favours light regulation.

Some companies will use VoIP connections to provide extra capacity for an existing PBX, but it's a good idea to check the price of the extra gateway equipment required. Anyone thinking of switching to VoIP for their phone services should think carefully about reliability and access to the emergency services.