Weird text messages appearing on Iphone 4

[phillipblue]

My g/f's phone has recently had the same strange text message appear as an unsent message on her iPhone 4. The message is VERY creepy about saying how they liked her profile, etc and it makes it sound like a stalker.  The message has appeared twice now - exactly the same.  Calls to Verizon only result in their saying it's impossible to hijack an iPhone and that they are baffled.  Both times the message appeared she was in possession of the phone so it's not like somebody picked it up.