Mobile giant Three says it will offer a superfast 4G mobile internet service from December — while Vodafone and O2 are switching on their rival services today.

Three says all its customers, new and existing, with a 4G-ready device will be able to get 4G at no extra cost. (See our Cheap Mobiles guide for the best deals.)

Those with an iPhone 5 can also get 4G on Three unlike O2 and Vodafone's services, which will not work with the latest Apple phone.

Initially, Three's 4G will only be available in London, Birmingham and Manchester. But the provider says its 4G coverage will roll out gradually reach to 98% of the population by the end of 2015.

It estimates over 1.5 million existing Three customers will benefit from 4G services by January next year.

Three will also continue to offer unlimited ("all you can eat") data as part of its tariffs.

How does Three's 4G compare to EE, Vodafone and O2?

EE launched the UK's first 4G network in October 2012. It added a premium of £5/month to tariffs to access the superfast service (see EE 4G launch MSE News story for more info).

Over time, EE has steadily cut its 4G prices, ahead of its rivals launching their services.

Prices for EE's 4G now start from £26/month for 500MB of data and unlimited calls and texts on a 24-month contract. EE's 4G service works on the iPhone 5.

Vodafone and O2's 4G services both launch today. They're both available to customers who upgrade to a new tariff (see Vodafone 4G and O2 4G MSE News stories).

O2's 24-month 4G tariffs start from £22/month with 1GB of data, unlimited texts and unlimited minutes each month. Vodafone's 4G prices start from £26/month on a 12-month contract, for 2GB of data with unlimited texts and minutes.