Siri not working on 3G

I just bought an iPhone 5S and just noticed that Siri doesn't work on 3G. It works fine on WI-FI, but when I'm on 3G she says she can't take any requests right now and that I should try later. I have to mention that I upgrated to iOS 7.1. Does that make any difference? Is anybody else experiencing this problem at this time or should I take it to the Apple store? Thanks.