My wife wanted something very similar. She wanted a blackberry because she uses the smartphone features (calendar, multiple alarms, etc) but had no desire for the data plan. However, all carriers began requiring the data plan on all smartphone purchases (see below for reasoning). My wife called AT&T customer service when she wanted a new phone, explained what she wanted and why she wanted it. Of course the person told her that they couldn't give her a smartphone without a data plan. She persisted, explained that she wanted, explained that she knew the limitations of the phone without the data plan, and reminded the person on the call that we had been a customer for 8 years. She also explained that the 'couldn't' wasn't a technical limitation, but an arbitrary rule. A few minutes later, she had a brand new blackberry being shipped to our address without a data plan.
The only cost associated with the data plans are additional towers. Each individual user doesn't add extra costs to the company - so the data plans are just cash in their pockets. It is also well known fact that it costs much more money to get a new customer than it does to retain one. Call customer service, speak to them civilly, and they will probably give you what you want. You may have to talk to a manager, but as long as they know you aren't an idiot and/or a jerk, it is much better for the companies bottom line to let you go on without the data plan than it would be to switch.
I've found that civility, knowledge, and persistance will work.
Why require them?
3 years or so ago, the smartphone market ballooned. There were ads on all TV stations touting the newest smartphone telling about everything it could do. So people would come in and upgrade from their razr (or whatever non-smartphone) to the newest smartphone expecting to have all this. The sales people told them they should get a dataplan to take advantage of all the features, but the idiots buying them didn't need the data plan - that was too much money. So these people took their new phone home and HOLY CRAP! it doesn't do anything it says on the TV. So they brought back in their 'defective' product because it wouldn't do what was advertized.
The phone companies were losing money because of returned phones that they now couldn't sell as new. That is why the data plan rule came into being.
If you buy a smartphone, you have to have the data plan to take advantage of the advertized features.