Instant cashback mobile phone deals offer a cash inducement for customers to take out a mobile phone contract. Retailers will pay back their customers a portion of the cost of the mobile contract in the form if "instant cash". The term instant is used to differentiate these deals from so called free line rental deals which are claimed back by redemption. With an instant cashback deal, you do not have to claim cash back at a later date, it is paid automatically. These deals are probably the most cost effective hassle free way to take out a mobile contract.