Hi @cjgarceau. Welcome to the community!
That's a very good question. In fact, when you change your phone number, your old phone number is released after 60 days and might be used by someone else on the network after a few months.
If someone that you know contact you using your old phone number, it will contact the current person with your old number or it might say that the number is no longer in service.
The old number will not reroute the call to your new phone number or let the person calling you know that your number changed.
Hope I answered your question. 
