I've Got Your Number by Sophie Kinsella

This story definitely grew on me.  I started out not liking the main character but as she evolved, I found her good points and began to root for her.  There are some great unexpected hidden twists and turns in the story line to keep it interesting.
The only part that bothered me was the constant mention to footnotes.  The heroine Poppy, is obsessed with footnotes.

The book begins with a crisis: Poppy has lost her engagement ring, a family heirloom from her fiance. In the frantic search for the lost emerald ring, someone swipes Poppy's cell phone but quickly finds (through the magic of writing) a cell phone in the trash, which she digs out of the trash and starts using. 

We then begin to meet the characters; her fiance and future in-laws (who are so scary-smart that she is intimidated), her work-friends, and especially the stranger to whom the phone originally belonged.

Give Poppy a chance.  If you don't like her at first, she will grow on you like a good friend.