How do you get wifi on wifi disabled 3g phones?

A wifi phone is just a phone that can use wifi. You would connect it to a wifi network to get a better signal for faster web browsing than a cell tower.

for sure, i use mine to make call

That depends on what you are planning to use the iPad for. An iPad Wi-Fi with 3g has both Wi-Fi and 3g connectivity, whereas the iPad with Wi-Fi only has Wi-Fi connectivity. 3g connectivity allows...

Actually, you can. What you need to do is purchase a MiFi adapter from AT&T or Verizon and sign up for one of their data plans.

If you go places and are willing to pay for AT&T or Verizon but if you don't then get the WiFi one because its not really necessary to spend the extra money for just 3G