It depends on if the rep. that added it backdated the change to the beginning of your billing cycle. If they did then yes, you will have all 500 messages and just be charged the solid $10 for that package on your bill. If they added it in the middle of your billing cycle then you will receive a prorated amount of the 500 messages dependent upon when it was added and then be billed the prorated portion of the $10 plan plus the $10 for the month in advance. Soooo...it all depends upon when and how it was added and how many of your 250 messages you had used at the point when it was added. Call 611 and ask them!! If it is a better deal for it to be backdated then see if they can do that!