I'd echo what Rogersea said - you'd get a better exchange rate in a formal money-changer than by paying $ directly. I've normally found the best rates in branches of Sanry's in Metro Manila.
Typical charge for using an overseas credit card in an ATM is 250php (plus whatever your card might charge). For some reason, certain bank ATMs don't seem to accept my VISA card - I stick to Metrobank and BDO wherever possible.
In rural areas, the ATMs do run out of cash quickly - especially if there is a national holiday or on/near month-end pay days. Also, many ATMs outside of Manila (those 'standalone' ones not built into the side of banks) run via an internet connection. Internet outages and brown-outs mean the ATMs all fail.
Be prepared to show patience whenever using a credit card - there's some stone-age mentality still around, with some salespeople having very little understanding of modern banking practices. Quite often, you'll encounter shop staff that don't know what 'chip and pin' is, or don't understand what a 'VISA Debit' card is (there's only credit card or ATM card, don't you know...).
Spent 15 minutes 'debating' the validity of an American Express card last month with a payment agent for concert tickets... because it didn't have "embossed writing".. and was therefore an ATM card...not an acceptable credit card.. Lady point-blank refused to even try the card in the machine, until her manager was called.
