What is the cheapest way to get a plan 4 a iphone or droid
Go with a no-contract plan. Which plan depends on where you are. In the US, try Virgin Mobile, $35/mo for unlimited data and text, 300min voice. Consumer Cellular has good family plans. If you are outside the US, google for "no contract cell plans."
Steal someone else's phone and use it as much as you can before they cancel. This costs nothing as long as you do it right.