If you use AT&T's GoPhone pre-paid service, you can use it without a data plan. If you don't use many minutes, it can be *WAY* cheaper than a post-paid (aka "regular") plan.
My wife and I use GoPhone lines (no unlocking needed, since it's an AT&T SIM,) with no pre-paid minutes, purely 10 cents per minute. My wife has the minimum data plan, I have the mid-range. We also use Google Voice as our incoming phone number, set so that it rings our cell phone plus our home phone simultaneously - so if we're home, we just answer the home phone and the call doesn't use any cell minutes. I do the same at work, switch it to ring my cell and work phone instead of cell and home. Plus, the Google Voice app allows unlimited texting for free. (But you have to use the GV app, and it doesn't do anything other than plain text. But Apple's own iMessages works for that between people I know are on an iDevice.)
We went from $150+/month to ~$45/month for the two lines. And we can turn data on or off, or increase/decrease the data plan on a per-month basis if we feel like it.