Vodafone's heavy promotion of its new 3G/GPRS datacard is welcome news to those who need to stay in touch with email and other business data while on the move.

When 3G was being defined we all thought its main driver came from mobile operators' need for new spectrum to cope with the growth in voice services.

As it turned out, that predicted growth slowed and the capacity of the mobile operators' GSM networks was instead expanded by adding small base stations. 3G was, of course, designed for data as well as voice and can provide a much wider range of data services than GSM.

It will be interesting to see how 3G will fit in with the other mobile or quasi-mobile services in the pipeline. There are three main wireless data technologies in this area. They are wireless LAN (WLAN) technology, used in hotspots; WiMax, for longer-range broadband services; and IEEE 802.20, for truly-mobile, high-speed data.

WLAN hotspots are appearing in lots of places but lack uniformity; a customer of one operator cannot access hotspots run by another. The mobile operators are in a very strong position to provide hotspots because of their existing network and billing systems. By using SIM cards, hotspot access could be just another line item on a phone bill.

WiMax is a common subset of the wireless broadband standards defined by the IEEE as 802.16 and ETSI as HiperMAN. WiMax kit is emerging and will provide data rates of about 10Mbit/s over longish distances. Again, the mobile operators have the base stations required, allowing them to compete with BT's wired DSL broad- band services. Later versions of the standards will allow some mobility for users.

The IEEE 802.20 spec now being developed uses techniques like those of 3G but develops them further by using adaptive antennas and collaborative base stations. Each mobile user is surrounded by a personal, radio cloud created by the intersection of several radio beams. This reduces interference and increases network capacity. Truly mobile rates of 20Mbit/s are possible.

So how do these systems fit together? I think WLAN hotspots will proliferate and mobile operators will soon have the lion's share of the market, especially if they can sort out user authentication and billing issues. It is more difficult to forecast the progress of WiMax, which may depend on whether 802.20 is delayed or proves too hard to implement for technical reasons.

I think 802.20 will be successful, however, and mobile, wireless data systems of the future will be based on 3G and 802.20, with WLAN hotspots where needed.