What's the cheapest way to get an iphone 4 right now?

I don't know much about phones and plans so i don't know if it would be cheaper to buy the phone used on craiglists and then get a plan or to get the plan and a phone from some company. Not sure what's the cheapest way to go. Any advice? What companies have the best plans?

T-Mobile no longer has contracts. You will not have to get a new 2-year contract when getting a new phone.

T-Mobile offers the iPhone 5 starting at $99.99 down payment.

T-Mobile offers UNLIMITED plans (messaging, calling, and 4G LTE data) starting at $50.00 / month.

See for yourself

T-mobile.com or e-bay! Best dealing site.