In case you've never read Pride and Prejudice we'll let you know one thing: it was written before cell phones existed. So Jane Austen's characters corresponded with letters, not texts, Facebook messages, or e-mails. Jane Hayes, however, smuggles her cell phone into Austenland in order to maintain some connection to the outside world.
It serves as a reminder that this Austenland thing is all pretend. The guests of Austenland are modern women living in bygone times. But Jane can't let go of certain modern conveniences, like the cell phone. This unwillingness to truly submit to the rules of Jane's fantasyland both helps and hurts her.
It helps, because she's able to use her phone to e-mail her friend Molly. As a result, she gets a background check on Henry Jenkins, the actor who plays Mr. Nobley. Without this Private Eye-style info, she might never have believed Henry when he says he loves her.
However, the phone gets her in trouble when her traitorous maid finds it and turns it in. It almost gets Jane booted from Austenland. However, Mr. Nobley convinces another Austenland guest, Miss Heartwright, to take the blame. Hm, we guess it ended up helping her in that respect too, because knowing that Mr. Nobley stood up for her makes Jane really, really believe in his love for her. We guess having a cell phone is always a good safety measure, even when pretending to time travel.