Non-US carrier Smartphone, is a data plan required?

[BigDanDizzle]

I am currently with AT&T. Prior to September 6th of last year, I was an avid admirer and user of smartphones. But since then, AT&T has imposed a required data plan for all smartphone users. I can understand the data plans will encourage use of smartphones to it's fullest extent. However, I, for one, don't really need it. I find it useless to pay for a service when I am exposed to WIFI everyday. Some time after September 6th, my smartphone (LG Incite) received some minor water damage and I was forced to use a feature phone for a short time. Once my smartphone was functional, I switched back. But, once I did, I received a text from AT&T saying that they will automatically add the data plan onto my next bill. I was thoroughly outraged. Since then, I've had a smartphone as paperweight, an expensive paperweight. I've just recently spoken with some of my buddies about this. One of them is currently with T-Mobile. He was looking to purchase a BlackBerry from eBay. I'm pretty sure that BlackBerry users must pay for their services. My buddy is like me and finds data plans useless. He told me that if you purchase a used smartphone from someone else that you can use it as you please without the expensive data plan. Is this true for T-Mobile? I've also researched this according to my provider, being AT&T. From what I read, it seems that if you purchase an unlocked smartphone that AT&T does not carry, you can use it without the required data plan. I know that the only way to get around this from AT&T is by buying the smartphone without the discount (for example; purchase an HTC Fuze for $400 or however much it costs with a 2-year plan as opposed to purchasing it for HTC Fuze for $99 with a 2-year plan). So, my question is; is a data plan required if I get an unlocked, unbranded smartphone? Will AT&T force a data plan on me if I do? What about with T-Mobile? Do they follow suit?