If you choose the credit card as your mode of payment, then you will pay 1 month advance of your plan. But in case your application was rejected, the cash will be returned straight to your account.
If you choose the cash naman, after application was approved mo na babayaran when someone from Air21 deliver your handset, you will pay the delivery man your 1 month advance.
I agree with @younggee Globe will not charge your credit card right away. Having a credit card will give you a better chance that your application gets approved. It is not a guarantee though.
If you live in Metro Manila or in a City and you have easy access to a Globe Business Center, please drop by if you have doubts with the online facility. Process your application there. Do not forget your requirements. You'll never know, you get approved right away and go home very happy.