TMO just tried Pay per Megabyte (1.99). Someone said they removed it and are no longer using it. You can get data banned on certain phones on your account. If you have no data charges, the amount will be zero. One of my lines phone is in England using an Orange SIM. There was no charge on that line. I also have a voice only user with a Nokia 6085. That can access data, but the user doesn't want to and I don't think he even knows how. No charge on that line either. I do have data on my line, but am usually under 10m since I most use my wifi. And I have no social apps or sync running.
My web browser will tell me I have to turn off wifi to access the network.
If it's a GSM phone, you should be able to access wifi with no SIM in the thing. I would turn on the Galaxy 3 just to see if I could connect. You just can't make a phone call unless you use VOIP. Same for text.