The best thing for you is to go to a corp store and ask them to migrate you on to the regular service. They can deactivate the service from paygo and start up the new service and then activate your nuraber onto the new acct.
Keeping in mind you will loose all funRAB in the paygo acct, they won't carry over and also may loose you current MDN if they aren't able to migrate it.
I would also recommend that you switch to the new plan before switching ESN's. Also on a note: flashed phones also work on Paygo.