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(Pocket-lint) - Vodafone will attempt to persuade its customers to upgrade to its 4G network next spring by knocking 70 per cent off their remaining contract. 

The Vodafone 4G Promise will see customers exchange any phone they have on an existing contract (so long as it's in good condition) with a 4G-compatible device, with Vodafone writing off 70 per cent of any charges due.

This comes as particularly good news, after it was revealed that the current iPhone 5 won’t work with either Vodafone or O2’s forthcoming 4G networks.

Customers who wish to opt for the 4G Promise must have been a Vodafone Pay Monthly customer for at least three months. 

Of course a large part of the appeal depends on how attractive Vodafone makes its 4G data plans.

EE, which will be the first operator to offer 4G network speeds from 30 October, recently revealed its own price plans and they don't come cheap.

For just 500MB of data for example, EE is charging £36 a month, while to get 8GB you’ll need to pay £56 a month.

Of course with more operators providing 4G network speeds, the cost of these data plans should become more competitive. 

Vodafone has announced that it hopes to provide 98 per cent of the country with indoor 4G coverage by 2013.

The Vodafone 4G Promise will be available to customers until 31 December 2013.

Do you like the sound of Vodafone's 4G Promise? Tell us why in the comments below...

Writing by Danny Brogan.