G1 Question

I just recently bought this phone off of ebay and slipped in my SIM card and everything works. I can make calls, texts, and even access the internet. I've heard that in order to do all this, you MUST be on the G1 data plan. So did I just automatically get switched over to that plan?

And since I can access the internet as of now (not through wifi either) am I getting charged for that? Really this is the question I want the answer the most to.

If you are on T-mobile and have another GSM phone with regular t-mobile data package. you will get charged the same rate. However if you have a blackberry plan, then you will be charged data rates.
I would suggest you get in touch with your provider ASAP, to avoid getting a shock when you get you bill!

Well I called Custmer Service and they couldn't even give me answer. The lady on the phone couldn't get over the fact that the phone worked by me just slipping in the SIM card.

The G1 works without a problem because it is most likely unlocked. i.e. not locked to a specific carrier. Some ppl that work at customer service aren't fully trained or don't get the full training. Most carriers don't even want you to know that you can get a GSM phone unlocked and go to another carrier.
I would call back and ask for a manager someone that knows what he is talking about.

Good Luck