You seem to be missing the point of the other replies.

You won't be able to use your device on T-Mobile and T-Mobile no longer has corporate discounts.

So its a full price phone $800 plus $38 activation fee plus $10 Sim Kit plus taxes and administrative charges and not including the plan cost.

So you will pay more in the long run.

Just buy the iPhone at full cost and you don't lose the unlimited data. If the costs are still too high for you maybe a prepaid phone might be a better idea. Unlimited everything for $45-$60

Good Luck where ever you end up.