How/Why Does Total Wireless Want Customers To Get A New SIM Card When You Switch Phones?

I have been a Total Wireless customer for a few years now. I came from post paid/contract Verizon and all of my smartphones were compatible with Total Wireless. I recall reading that Total Wireless wants users to get a new SIM card each time they switch phone. However, I have also read that people have activated a SIM card in a phone and installed it in a different smartphone and everything works fine.

So, I am just wondering why Total Wireless wants customers to do this each time? I gather that they have no way of enforcing it, since swapping SIM cards has worked for some customers in the past.

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