Sainsbury is claiming a world first' with the launch of a mobile phone service which, it said, will give customers the cheapest calls available. Sainsbury'sOne, which goes live in January, will check customers' calls against the standard tariffs of Cellnet, One2One, Orange and Vodafone. Pre-pay users will either purchase a Sainsbury'sOne phonecard or top up their phone using a credit or debit card. If their quarterly statement shows Sainsbury'sOne to be more expensive than any of the networks, the customer will receive Reward points to the equivalent monetary value of the difference between the Sainsbury price and the lowest of the four networks. Post-pay users will receive a monthly invoice and will be charged the lowest price of the four totals shown. Sainsbury marketing director Sara Weller said: "This will be the biggest shake up the UK mobile phone market has seen." {{NEWS }}