O2 has joined the growing number of UK networks with a 4G service, launching today in London, Leeds and Bradford.

The network will gradually expand to include Birmingham, Newcastle, Glasgow, Liverpool, Nottingham, Leicester, Coventry, Sheffield, Manchester and Edinburgh by the end of the year, with the aim to reach 98% of the country by the end of 2015.

New and existing customers can now pick up a 4G contract in store or through the O2 website, with a range of tariffs starting from £26 a month.

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These all include unlimited calls and texts, with data allowances starting at 1GB and reaching 8GB on the most expensive contract. That may come as a disappointment to anyone hoping for unlimited data, especially as EE , the UK's first 4G network, has much larger data bundles for those willing to pay for it.

To add some incentive for prospective customers, O2 will be including twelve months of free music and videos on O2 Tracks, along with multiplayer games that don't eat into data allowances due in the coming months.

Additionally, O2 customers that bought an iPhone 5 can upgrade during their contract to get a new 4G-compatible phone at any time, with the network paying 25% of the cost of the remaining line rental. O2 Recycle will also earn them up to £295 with a trade-in.

Company CEO Ronan Dunne said "Today marks the first step in our ambitious plan to bring 4G services to millions more people across the UK.

"The mass-market arrival of 4G marks a new generation for the digital age and we’re excited to be celebrating the occasion today with our customers."

We'll be taking a closer look at O2's 4G network in the coming weeks, to see how it compares to the newly launched Vodafone service and EE's existing 4G network.