Ditto to the last two. Larry said the minimum purchase requirement they tie to a retention bonus depends on spending history. If yours shows you've been using the card a good deal, no requirement.
He also said that a month, for this purpose, isn't a billing month or a calendar month. Rather, it starts when you register for the bonus - so, since I registered today, mine runs from the 10th of one month through the 9th of the next. If that matters to you, you might want to schedule your call accordingly.
And thanks to FT for this too - if it weren't for these threads, I would never have heard the magic words "retention bonus!"