Nice way to encourage new members.
Now to answer the op question.
You will need to buy another phone. Cancel you other sevice.
GSM phones do not work for the Verizon network.
If want to use Verizon. He could get an inpulse phone from wal-mart or Verizon website.
You could also use one of Verizon MVNO
pagepluscellular com I use them myself. They sell page plus phones on their website and at village pantry. However, airtimes pins can be bought online, and at speedway service stations.
There are other Verizon Mvnos but you will need a
CDMA phone. Carefull on buying those. Airvoice and others.