The second will be up to two Mbps for local area/low mobility data. That compares with fastest internet access on fixed analogue systems of around 56kbps and 128kbps on ISDN.
The new 3G networks will cost upwards of £1.5bn each to build.
Operating to an international set of standards known as Universal Mobile Telecommunications System (UMTS), they will deliver up to two million bits/sec (Mbps) bandwidth.
This is 200 times what is currently possible on a mobile phone. It will allow a step change in delivery of fast internet services, promising such new benefits as:
The second will be up to two Mbps for local area/low mobility data. That compares with fastest internet access on fixed analogue systems of around 56kbps and 128kbps on ISDN.
The BBC has had an early look at some of the first prototype 3G devices, operating under realistic conditions on a small, experimental UMTS network.
The initial demonstrations on a video-capable phone looked impressive.
Real-time video images using MPEG4 compression were displayed on a Panasonic handset and looked sharp, only breaking up a little if the caller moved suddenly.
The packaging for the handset was still relatively bulky and it overheated easily, but that is hardly surprising on such an early prototype. With up to two years available for development before real handsets are marketed, further improvements are inevitable.
Consumer interest
Ericsson, a major suppler of the infrastructure needed to equip the new networks, has been operating the country's largest UMTS test facility for the past year.
The BBC was shown a handful of applications, ranging from video e-mails to interactive gaming, which clearly showed the networks have potential to deliver a wide range of novel services.
The demand for these services is still unclear, but the industry is confident that the first wave of internet capable mobile devices based on the Wireless Application Protocol (Wap) will prove highly successful - and that will in turn lead to a wave of consumer interest in the 3G devices that follow them.