As far as I know it's mostly in Tagalog-speaking areas.

In Bisaya they say Ate or Kuya, or ma'am/sir. A lot of the time it's 'ma'amsir' as one word, whatever the gender.

You hear it everywhere in Luzon, but hardly ever in Mindanao.

There are a lot of languages and dialects in the Philippines. Po and opo come from Filipino, which is the official language besides English, and it's mainly spoken in Metro Manila. So you hear it a lot in Luzon, especially in the NCR. In the Visayas and Mindanao you rarely hear it, because they have their own languages and dialects. Instead of po and opo, they show respect by calling you kuya, ate, auntie, uncle, or whatever their own language uses for someone older. So don't be offended if someone calls you kuya/ate even when they're obviously older than you — calling someone by their first name is seen as somewhat 'disrespectful' here, unless of course you prefer it. And if they call you 'hoy', that's obviously rude. But most people, especially the older generation, call every white person 'Hey, Joe', and it's not meant as disrespect. It's their way of making friends or getting acquainted. So if someone doesn't use po and opo with you, it doesn't mean they're being rude — it's just not their language.

It's used more with older people, or when you really want to thank someone. 'Thanks so much' becomes 'thank you po'. My wife and I use it when we're trying to talk each other into something. She'll say 'Ramon po?' and I'll answer 'Mexican po?'

The Visayas do NOT use po or opo. But you do use it when you're in Luzon. So it's not nationwide.