Orange is paying Ericsson £37m to build a "high-speed" General Packet Radio Service (GPRS) network by the end of this year.
However, Orange said the data speeds possible would not match those previously promised by Ericsson and other handset makers.
Last year GPRS was touted by the industry as being capable of 115 kilobits per second (kbps) and was seen as a major step towards third generation services.
These would eventually allow users to send and receive data at up to 2 megabits per second.
Now, because of technical problems with GPRS - which offers an always-on connection without having to dial up each time - the handset manufacturers are scaling back their claims.
An Orange spokesman said the Ericsson handsets would offer "up to" 26.8kbps through a double-slot frequency solution.
Ericsson has promised a four-slot phone offering "up to" 53.6kbps at the beginning of 2001, said the spokesman.
Today's mobile telephones work at 9.6kbps, so the step-ups being promised are not as huge as first suggested. The manufacturers are still trying to overcome the problem of higher GPRS speeds causing phones to overheat, and hence reduce battery life quickly.
Motorola claimed a first at this year's Cebit show with the launch of a single slot GPRS phone.
Other operators have promised GPRS roll-outs this year, but, unlike Orange, they have not specified data speeds.