Can you jailbreak an iphone 4 on t-mobile network without a data plan?

Will it work without a data plan? I have a 3gs and its jailbroken and still works without a data plan.

No. You need a data plan.

Whether a phone works without a data plan has nothing to do with whether it's jailbroken or what kind of phone it is - it's all up to the carrier (phone company).

The reason the 3gs works without a data plan probably is because the SIM in it doesn't have a data plan, and the carrier that activates that SIM doesn't know or care what kind of phone the SIM is in.

I suggest you to see this
http://unlockappledevices.com