I've Got Your Number by Sophie Kinsella

Poppy loses her cell phone.  She is at a total loss.  Amazingly she finds a phone in a trash bin and starts using it.  This leads to a crazy interaction between her and the company that owns the phone.  There is much forwarding and many misunderstandings.  As Poppy does things you can tell it is going to get her in trouble and you are practically begging her to stop.  Kinsella tells a great story, keeps you going and wanting more.  Great book!!