I used to have to do this when I was using my xv6800, I think any time I changed the radio. If you flash a new ROM that includes a radio, this process needs to be redone. As a side note, none of this EVER needs to be done with a 4G LTE device, as the SIM card handles all account settings and authentication data (A-Key stands for Authentication Key).
You will need an ESN from another VZW phone that is NOT active on any account (I will call this the "old phone").
- Log into you account on vzw.com
- Change ESN on your account the the ESN from the "old phone"
- Change ESN on your account back to the ESN for the "new phone"
- Dial *228 option 1 to program your phone. This will set the correct A-Key
When you change the ESN on your account, VZW will generate a new A-Key in their HLR (Home Location Register ... See wikipedia for more info. It states GSM in the article, but the same applies for CDMA). The *228 option 1 will ONLY program the A-Key if the HLR thinks that it has not been done yet, therefore switching ESNs will allow the A-Key to be programmed into the handset.
And for the record, I don't work for VZW and never have.