[OrBy]

One way to prevent this is to edit or create a custom PRL based off the curent Sprint PRL that removes the carriers that you don't want to roam on. QPST has a RL (PRL) editor that can be used to do this but as to the method of actually doing it you would have to ask some one else. Once you have done this simply drop the PRL onto your storage, go into ##778# and then update it from the PRL menu and reboot when promted. I have never done this so YMMV.