By Paul Sandle

LONDON (Reuters) - Sky said it would enter the UK mobile market with a SIM-only deal that allows data allowances to roll over each month, and offers free calls to the 11 million British households that take its TV services.

It was "time to shake up" the mobile market, particularly in data, where many customers paid for more than they used because they were worried about exceeding their allowance, the pay-TV group said on Tuesday.

Sky is the last of Britain's big four broadband providers to offer mobile to its customers, giving it the full "quad play" offer, which also includes TV and fixed-line telecoms.

Stephen van Rooyen, Sky's UK and Ireland chief executive, said the company had asked more than 30,000 potential customers what they wanted from a mobile service, and more flexibility on data was top of the list.

"We've designed it based on what people told us they want - it's easy, flexible and transparent and it puts the customer in control," he said

He declined to give any targets for customer sign ups, but said Sky households had on average two mobile contracts each, giving a potential market of about 23 million.

BT bought EE, the biggest mobile network, earlier this year, while Virgin Media uses EE's network to offer its own branded mobile and TalkTalk is switching from Vodafone to Telefonica's O2.

Sky is also piggybacking on the O2 network, although it will issue its own SIM cards and handle all parts of the customer relationship.

Mobile customers will not receive a combined bill for all Sky services, however, as the company said customers preferred to keep an individual relationship with their mobile provider.

Sky is offering three packages of 1GB, 3GB and 5GB of data a month priced at 10 pounds, 15 pounds and 20 pounds, respectively, with free calls and texts for its TV customers.

More than 46,000 people had already registered, the company said, adding it would launch a full marketing campaign in the new year and offer handsets from next spring.

Analysts at Morgan Stanley have said entering mobile should be a positive for Sky.

"Sky's got most of the infrastructure in place, is good at cross selling, it's a 15 billion pound ($19 billion) market and Sky doesn't need to get involved in handset subsidies," they said.

($1 = 0.8001 pounds)

(Editing by Alexander Smith)