Siri's clearly the flagship feature of the iPhone 4S, but is talking to your phone doing damage to your data cap? That's what Ars Technica investigated, asking Siri to do things like set an alarm or look up the number of calories in a muffin and tracking the data consumed.  The tests showed that if you use Siri a few times a day you'll be using somewhere between 3.7 and 5MB of data a month — of course, there's more data required to do a more complex search, or to send a long message, so usage can vary in a big way. Ars also only has a single day's worth of data (11 queries in all), so we'd like to see a longer-term study back up their extrapolation, but either way, it looks like those of us with smaller data caps should always Siri responsibly.