Not with an 8100, that I know of. There are some confirmed tricks for Rogers and China Mobile. If you had a model with wifi then yes. Why don't you want to pay for a data plan?
I'm pretty sure there's no option to connect without paying. You've got to use your carrier to make the connection so their network has to authenticate you. If there is a way it's not blackberry specific as network access is allowed or disallowed on the server and not your device.
Posted from my CrackBerry at wapforums.crackberry.com
If there was a way we'd all be on the band wagon. The unfortunate fast is that we all have to pay
This is true, looks like you're going to have to cough up the dollars or just carry around an amazing device without being able to use most of it functionality. Your choice.