purchasing used 5g gateway for home internet

My concern with cancelling at the end of the season is less about keeping the phone number and more about keeping your slot in the area for internet. The T-Mobile Internet availability is based off of bandwidth availability. If you cancel one year and then more people activate over the winter, when you go back the next summer there may not be any more slots available, and you could miss out on having T-Mobile Internet at that location. Ideally, we would like every home to have our internet, but we also want to make sure the experience is good so we limit the number of activations to prevent overloading the towers. 

I double checked our seasonal suspension requirements, and I don't see anything about Internet lines not being eligible. You can suspend the line for two 90 day periods within 12 months. That means that you would pay full price for half the year and $10/month for the other half for that line. I don't know why the person may have told you that it was not able to be suspended unless you were trying to suspend it for a third 90 day period. 

Hope this is helpful.