Yes, that's right, as far as the SIM goes. Once you get the iPhone, you want some combination of:
- a personal voice plan (since you're an existing customer, do this through a customer service person -- don't just do it online. You deserve a better deal. E.G. My current deal is $39.99 for 1000min/unlimited nights and weekends. They started offering that deal relatively recently for $49.99, but I've had it at $39.99 for more than two years now).
- T-Mobile Unlimited Internet ($19.99), which includes hotspot access
- A messaging plan if you want one.
So I pay a few cents under $70, inclusive of fees, for 1000 min, nights/wknds, 500 SMS / mo, unlimited data, and hotspot access. You can change all those plan details without renewing your contract. You might not even need to start a contract.
You should also ask if you can just convert your existing account to a single customer account without a new contract. You may be able to do that.
If not, my advice would be to order a phone that doesn't cost you too much, but for which there's a good used market, and then just re-sell it at a profit. E.G. buy something you can get on contract from T-Mobile for $50 or 99 (that part may also be negotiable) and then turn around and sell it off for $200 or more. There are typically some smart phones and so on that you can do this. Maybe the new RAZR in a cute color. You can check on eBay for what's easiest to sell....