How do I have access to all data features without data plan?

[Peders]

I just purchased a used G1 today, put the sim from my non-data phone into it, signed into gmail and presto I have full internet access without wifi!!!  Wifi is completely turned off.  I can get to different websites - salon.com, google.com, ibm.com.  How is this possible?  I logged into my tmobile account and I verified that I DO NOT HAVE A DATA PLAN.   Is there a free trial period where you can use data for no charge?  I haven't run into any postings where anyone has experienced this.  Most people need wifi to access data features if they don't have a data plan.  I was planning on getting a data plan but for now it looks like I am getting data for free.  Someone please explain.

Thanks..

 

[imsobased]

Same with me actually and i was about to post this lol. Right now i have a samsung gravity phone with no data plan and my brother and sister have the my touch 4g. Since my bro has one, he gave me his g1. When i put my sim from my graivty into the g1 it made me create a google acc first, and then i was able to use the phone and got full service. The internet also worked but i didnt use it since i didnt want to get charged for it. After a day i put my sim back into the gravity because i got paranoid that i might get charged a lot extra. So, my question is if i use my sim in the g1 and basically use it just to text and call would i be getting charged anything  more or would it be basically like using a regular, basic avg. phone.