Plan 999 has a subscription cost of Only Php 999.00/month but you can use and equivalent of Php 1700.00 in value which you can use for combos, a gadget and consumbales. More than that amount as well as value added services would be charged on top of that Php 999.00.
Regarding Plan 999, It has a PESO VALUE (PV) of 1700.
From your 1700, the peso value equivalent of your gadget (which is usuall 600), will be deducted.
So you have 1100 PV Left for combos and consumables.
By default, if you have not availed of the higher internet combo which is GoSurf 999, you can choose to opt for GoSurf 99 which will again be deducted from your remaining 1100PV. So if you decided to get Gosurf 99, you will have remaining of 1001 of consumable which you can opt to use as full consumable or you can get combos. Refer to this http://www.globe.com.ph/combos-and-boosters for the complete list of combos and boosters.
So if you choose to have the 1001 as full consumable, that you have consumable load of 1001 for regular calls, texts, and browsing.
For VALUE ADDED SERVICES (VAS) like unlimited calls, texts and internet surfing promos, that will be billed on top your Monthly Recurring Fee (MRF), which means it is on top of your bill of 999.
If you have also consumed all of your consumable of 1001, and still use the service, anything in excess is billed on top of your bill.
I hope this has helped you.
Thanks and best regards!