O2 has announced that it will launch its 4G LTE mobile network on 29 August, becoming the first competitor to EE to roll out the service in the UK.
EE became the UK's first 4G network in October 2012, after Ofcom allowed it to use its existing 1,800MHz spectrum for 4G service.
Since then the UK's other networks have been racing to catch up, purchasing their own spectrum in an Ofcom auction in February.
O2's parent company Telefonica paid about £550m for its 4G license, which will use the 800MHz spectrum.
O2's LTE service will initially only be available in Leeds, Bradford and London, though it plans to extend that coverage to 10 more cities by the end of 2013. It said about 5 million people will be covered at launch, with 2 million more added every week.
The network will offer much higher data transfer speeds that 3G, though it will be limited to certain handsets - not including the iPhone.
It has been known for months that O2's network would not be compatible with Apple's flagship handset, though the company's CEO Ronan Dunne said he would be "gobsmacked" if the issue was not addressed by future Apple products.
It is also likely that in some areas where EE has been able to install upgraded equipment O2's 4G speeds will lag behind its competitor's.
O2's lowest tier 4G tariff will cost £26 a month, compared to £21 a month for EE's lowest basic rate for voice and data - though it's not known exactly what will be included in those prices.
O2 said 4G customers would be given "free music content" for 12 months - though what that entails isn't clear.
However, O2 has confirmed that like EE it will offer no "unlimited" plans, disappointing users who use large amounts of data - or would, if they had the option.
The other UK networks are expected to launch their own 4G services later this summer.
In a statement Ronan Dunne said:
"It’s great that I am able to announce O2 4G the day after the spectrum has been cleared for use. Digital connectivity will be made ubiquitous by 4G and become the oxygen of modern life. It is our intention to use 4G to inspire the nation through the possibilities of technology, encouraging people to live more, do more and be more with O2.
“The full potential of 4G is as yet unexplored, but what we can be sure of is that it will allow for a whole new world of opportunity that people are now ready for. Over half of our customers say they use more data than two years ago and even more use wifi wherever they go, to always stay connected. Given this trend, there is no doubt that 4G will transform our lives, be it as consumers, in business or through public sector services.”