Is a boost mobile sim good in a sprint black berry 8830?

Only if the blackberry is unlocked from the origional carrier. Sounds like your phone is still locked. Contact the carrier and if you are in decent standing with the company, they will provide a sim unlock for the device.

You can either call Sprint support to obtain cose, they may give you the code, it takes between 1 - 3 weeks to get the code fromt hem, or you can use online unlocking service where you can unlock your mobile with in hours.
I would recommend mobileunlockingcode , as their prices are excellent, fast turnaround time and best customer support, secure payments from paypal, make them top company in the industry.
Thanks