Well, I also think that the iPhone data plan is the same price (if not a little cheaper) that a regular unlimited smart phone data plan.
As far as putting your sim card into an old phone, your iPhone SIM will work in any GSM phone. Unfortunately, that cannot be said about any GSM SIM, which is why unlocking is so popular.
**Holy Crap! Has anyone looked at the prices for data on AT&T's website? Data alone is EXPENSIVE.
But it get's stranger still. I went and selected a national450 plan, the LG Neon, and then it gave me my data add-on options. The first one is Unlimited Data and Messaging for $30. What the hell am I paying extra for messaging for? **
It might work for a while but they r gonna catch up. My friend was using his sony ericsson, with a regular cell phone data plan with an unlocked iPhone (something like 20.00 for unlimited data and text) and one day he got a bill with the iPhone data package. He really wanted 2 keep the iPhone so he had to sign the 2 year agreement with ATT and start paying the 30.00$ data plan + text