If you bought the phone outright (& paid the $1,000+ US or the international equivalence), it will be unlocked at the start.
If you paid anything less (like an upgrade on contract or on an installment plan), it's likely locked to the carrier you purchased it with until the contract or installment plan is complete. Once any carrier interests are met, you can submit an unlock request.
Beyond that, iPhones in general are considered a "world class" smartphone as they're designed to work with all the major cellular frequencies & standards (GSM & CDMA) throughout the world at the time of it's release... so you should NOT have any problems using the phone that was purchased in Japan, the US, England, India or anywhere else within the Philippines. However, you'll likely need to see about getting a SIM card from a cell company from that country to avoid International Roaming charges (as it's generally cheaper to "rent" a SIM card with a local carrier of that country than purchasing Roaming packages from your carrier).