If you've tried to get in on Square's mobile payment system, you know that a critical part of the whole setup is the tiny credit card reader that plugs into your phone's headphone jack -- and in all likelihood, you don't have it. The company just sent out a message to those who've signed up for their service today, saying that a prior hardware shortage is resolved but that it's only half of the problem; the other half, and arguably a more serious one, is that the company needs to find a way to "handle the huge demand for readers and still manage the risk of chargebacks and fraud." So far, those risks have been mitigated by
