I guess you are talking about google voice?
this lets you answer your sim card phone number any place (inside the US) were there is wifi and no cellphone coverage from anyone not just another apple device. Say a big brick building, underground like subways, etc etc
No, I'm not talking about Google Voice. Previous to today, I just turn on WiFi and use my internet connection to make calls via my iPhone. I'm trying to understand why this way anything different. I guess it really isn't.