Sky has officially announced its entry into the mobile network market with Sky Mobile, its first 4G service.

It is initially offered with 12-month contracts and SIM only, although phones, such as Samsung devices and iPhones, will become available in 2017. It is also designed to be simple to understand, with three different price points for data.

There are also simple prices for calls and texts. If you opt to “pay as you use” it will cost you 10p per call minute or 10p per text. Or you can pay £10 per month for unlimited calls and texts.

Sky TV customers, however, get the latter for free. And it applies for up to five SIMs per household.

They will only pay for the data, which is offered at £10 for 1GB per month, £15 for 3GB per month or £20 for 5GB per month.

Where the Sky Mobile deal differs from plans from other providers is that if you do not use all of your allotted data allowance, it rolls over. Some do roll over data to the following month, but Sky’s will be available for use for up to three years.

It is also cumulative, so you tot up more in reserve every month you use less. You can cash in your reserve data 1GB at a time.

Sky is offering other incentives too. Even though its plans are contracted for 12-months, you are free to change your plan up or down each month, so you can opt for more or less data allowance depending on how much you use.

The final incentive, called Sync, allows Sky TV customers to sync their home TV planner with their phones through Sky Go, to watch anywhere they like – over Wi-Fi, 4G or downloaded for offline viewing. It effectively gives Sky TV customers free access to Sky Go Extra.

This will be limited to Sky+ subscribers only at first, but Sky Q customers will also get it in the new year.

Sky Mobile is now available for pre-registration, with the first customers receiving their SIMs before Christmas. A more general release will start in mid-January.