Help Grandfathered sidekick LX plan


My girlfriend has the 09 sidekick LX with the unlimited data plan on it. I have done a LOT of searching and I have gotten mixed answers on weather or not she can use her current sim/plan in a G1. If there is a workaround I am up for it, but before we buy the phone we would like a definitive answer.

I am sure this has been asked many times and i apologize, but I have just seen so much conflicting information.