If Tello indicates the phone can be activated, then the problem is on the Virgin Mobile end.
The solution is to contact an agent and try to have the IMEI authorized in the database.
Ways to do that include sending a PM message here, or contacting agents on Twitter or Facebook.
Unfortunately, it is not an issue you can resolve yourself.
Just keep an eye on the 14 day return period if the reason for the purchase was to use it exclusively here.