It's not always the current month and the next month. It only does that when you sign up for the contract near the end of a billing cycle. If you want to avoid that then find out when the billing cycle ends (I want to say it's the middle of the month-ish) and go as soon as the next one starts.
as for the plan, the minute plan you want is $40 and the iPhone data is $30, so that's $70 -- plus you say you want unlimited texting, so that's an extra $20 a month. You're looking at $90 a month, plus the $199 for the phone, plus the $36 activation fee (if you can't get it waived). The activation fee is on your first bill though, so you only have to pay for the price of the phone and tax when you actually buy the phone.