My husband's dad went by Pops to his kids and now Papa to the grandkids but it isn't very common for a dad to be Papa where I live except with Hispanic cultures. My FIL is from OK but I don't know if it is a more popular name there too.
Well my kids call me Mama, hence part of my screename. My kids call my husband dad. They call my dad Papa. But I know where I'm from its not uncommon for people to call their dad Papa. My grandmother always calls my husband Papa when talking to the kids about him (she visits us a lot-about once a month) and it confuses the heck out of them.
I always called my dad "dad" and my grandpa "pappy".