Prepaid plan while paying for EIP?

I'm not sure if this'll work or not since I don't see anyone else doing it, but I have an idea. I'm on a 3-line family plan on Sprint with corp. discount for about $160, and I'm looking to switch to T-Mobile. Problem is, with the new plans we'll be paying about $210 ($150 for unlimited everything and $20 each per person for monthly phone payment). So I'm thinking we'll just:

1. Get the family plan with the phones

2. Cancel the plan but still keep paying monthly for the phones

3. Get the $30 prepaid plan for each person.

So that'll be around $150. It's a little cheaper but at least it's better than Sprint. Will this work?