Why bother even getting a data/Internet-capable device without the data plan? No data makes it a very expensive brick that makes phone calls.
You are only required to take a data plan with T-Mobile if you buy the phone from them at a discount (with a subsidy). All carriers do this, as it's a good way for them to recover the subsidy on your phone. If you bring a data-capable phone to the carrier and take a no-contract plan (which T-Mobile does offer), they cannot require you to get a data plan.
The problem with that scenario is that you have to already own the phone or you have to buy it at the full price. This is actually cheaper over the long term then having a contract plan, but that's another story.
The Android phones require a data plan because you have to connect to a Google account when you first set the phone up. So, without the data plan, you wouldn't even be able to use the device on the network.
Now, you mentioned that you had a Bold you got from AT&T, right? Well, you can sign up with T-Mo and use that phone if you want. Tell them you want an Even More Plus no contract plan (you can see the details on their website). Select the features you want and they'll set you up with a SIM card, drop it in the phone and off you go. Later on, when you decide to pay for the data plan, you can add it or get a new phone.