Siri may gobble up some of your iPhone 4S' data plan, but fortunately she's not an overeater--just a bit peckish.
Ars Technica conducted a pretty thorough investigation into just how big a dent Siri users can expect the digital dame to make in their monthly data usage. See, whenever you talk to Siri, an audio file of your command is sent to Apple's servers for processing and then the requested data and vocal response is sent back over the network to your phone, even if the question is something that should be able to be gleaned from your phone's local data.
The results are pretty clear--unless you're attempting to have an intimate relationship with Siri and you're on the emotionally needy side, she's not going to blow out your monthly bill. Ars found that each Siri query ate up about 63KB of data on average, although naturally that figure will vary for different users and uses. Here's what Ars found when it extrapolated that rough amount out under different monthly usage scenarios:
If you use Siri 2-3 times per day at an average of 63KB per instance, you might expect to use 126KB to 189KB per day, or 3.7 to 5.5MB per month. For 4-6 times a day, that might come out to 252KB to 378KB per day, or 7.4 to 11MB per month. If you use it 10-15 times per day, you might end up using 630KB to 945KB per day, or 18.5 to 27.7MB per month.
So, 27.7 MB per month is a little over 1 percent of a 2GB plan, probably not worth giving Siri the silent treatment for most of us. Let's also not forget that you can query away all you want over a Wi-Fi connection without nibbling at your monthly data allotment.
Of course, how much time you spend with Siri may depend more on other factors, so long as she's living in Apple's servers rather than the iPhone itself. In my case, the single bar of EDGE network coverage I receive in the far corner of my office greatly restricts the potential for our relationship. CNET's Dong Ngo offers a great in-depth look at real-world data speeds for the iPhone 4S to provide a little insight into just how close you and Siri can grow to be. Check it out to so you know if you should be preparing your speech now--"Siri, it's not about you, it's about AT&T."