That depends on the approver your application, when I applied for my postpaid plan before which is Plan 999 my basic salary is around 25K. Since you were inform that you will need at least 30K as a basic salary to apply for the iPhone 4S under Plan 999 which you mention you don't have. The only option to get the device and plan you wanted is this.
If you have no proof of income: You may choose to pay a 1-month Monthly Service Fee in advance via your credit card, get an existing Globe subscriber as a Guarantor, OR you can pay your Monthly Service Fee 6 months in advance.
For more detail on how to apply for a postpaid plan, you can refer to this link Postpaid | Help and Support.