How to Buy Airtime from Guarantee Trust Bank: Simply dial *737*Amount# Example: If you wish to recharge N1000 you simply dial *737*1000# then you’ll be recharged with N1000 and N 1000 will be deducted from your bank account. With Guarantee Trust Bank, you can as well transfer airtime to other sim cards that are not registered with your bank account. Like to friends and loved ones. Simply dial *737*Amount*Recipient Phone Number#, after that you’ll be asked to choose the network that your friend uses, then lastly you’ll be asked to input the last four digits of your ATM card.