1. go the virgin mobile's website and activate the phone. You will get the phone number (based on your address) and MSID number. you will need these.
2. Come back to the phone. Press ##virgin#, press Yes to confirm
3. Instead of "Activate the phone", choose edit. you will see some random number, erase that (using BACK button) and type your new phone number.
4. press OK, you will see another random number. Erase that and type your 10 digit MSID number (ignoring potential leading zeroes).
5. Hit OK and you are done.
They tell you (if you call them) that it might take up to 4 hours to activate, but mine activated instantenously. Good luck!