You will have to keep it for a full 30 days to do that (otherwise you have to return the phone). And that means you will also have to pay your first month's bill in full.
But yes, you can technically do that.
Don't plan on activating it with AT&T again for 90 days after that though.
You're looking at $335 for the phone w/ activation, plus taxes if they apply where you are. $175 for the ETF. And a minimum one-month bill of $69.99, again with fees and taxes.
So all in, if you do not pay tax you're looking at $579.99, or $605.12 w/ 7.5% sales tax.