Although this might sound like I'm trying to cover a dodgy request with an anecdote, I swear this story is legit.

My friend has had this guy at Uni stalking her for quite some time now, so she's taken to ignoring his txts, emails, etc. However, the other day she received a txt from someone in her phone book, let's call him John. Anyway, John was saying some odd things so she replied saying "Oi John what have you been smoking", and John replies, revealing himself as  this stalker dude! Yet it appeared to come from John's number! She also said the "callback number" was really long and odd. 

So my question - is this Telecom's network/her phone (She has one of those RAZR-like Sanyos) screwing up? Or is this guy really creepy and is this sort of thing even possible?!

Thanks on her behalf for any advice :)