Yes. When you do a phone swap everything inside your Virgin Mobile account will be transferred to your new phone such as phone number, plan, minutes, and any balance in your account.
Here's Virgin Mobile's answer from the FAQs:
Swap your Virgin Mobile phone online
If you're a current Virgin Mobile customer and you've bought a new phone, you'll need to do a phone swap to switch your mobile number to the new device. There is no charge to complete this transaction online.
Simply click here to log into My Account [MANAGE MY ACCOUNT at the top of this web page] with your phone number and 6-digit PIN. Choose Swap Phones from the 'I Want To...' menu on the right of the Account Overview tab. Next, you will need to enter the ESN number from your new phone and follow the steps to complete the phone swap.
Customers who purchase a Blackberry phone must complete the phone swap with a Live Advisor at 1-888-322-1122, with no additional cost.
• Virgin Mobile now takes trade-ins on certain phones. When shopping for a phone on this website click on the GET PAID TO TRADE tab. See the following page
for details: http://buyback.virginmobileusa.com/vmb/select