For those who need Visas and did not get them before leaving, depending on your citizenship they are available right at the airport (Term. 1 at least) upon arrival, and the office is open 24 hours/day. I believe that's more expensive than going to a regional office but it is convenient.
Email response from Manila Immigration Bureau: "As the holder of US passports, you may enter the Philippines visa-free and may be admitted with an initial authorized stay of 21 days provided you present passports valid for at least six months and return or onward tickets. Upon arrival, you may apply for a Visa Upon Arrival (VUA) at the airport. For the VUA, there is a payment of $50.00 Visa Fee plus P500.00 Express Fee and P10.00 Legal Research Fee. Thereafter, you may apply for one-month or two-month extensions one week prior to the expiration of your valid stay.
The counters and cashiers are operating 24 hours / day at the Ninoy Aquino International Airport."