Royal Bank of Scotland's customers who use the bank's cash machines over the next month to top-up their mobile phone stand to win one of six prizes worth £150 of airtime.
The ATM mobile top-up service has been available for Orange, Vodafone, O2, T-Mobile and Virgin Mobile network users since April. Customers can use any of the bank's 1359 cash machines to pay for air-time on their accounts.
The bank says the service is already proving popular. The new incentive scheme, which will run from 17 May to 11 June, is designed to encourage wider take-up.
It follows a more generous promotional programme late last year in which the bank randomly loaded six 'golden tickets' worth £10,000 each into its national ATM network.