Can I Use a Post-Paid SIM card in a GoPhone?

I currently use a blackberry 9700.  It is starting to go downhill and I want to get a new phone before it breaks and im stuck without a phone.  My upgrade isnt for another year, so I was wondering if I could take my post-paid SIM card from my blackberry and put it in a GoPhone (the LG Thrive specifically) and use it as a regular on-contract phone.  And if this is possible, would I see any change on my wireless bill (i curently have the least amount of minutes, unlimited text messaging, and the largest data plan [i believe it's 2GB]).  Thank you in advance for your help.