Option 1 - Dial 141 before her number (to make it withheld) and call her at 4am. Hopefully you'll reach voicemail with a personalised greeting. Alternatively, call when you think she might be on the underground or out of reception.Option 2 - Get a friend to call and then launch straight into "Hiya, I've got the presentation ready to go, in a bit of a rush but do you want it sent to Michael or David or both?". She'll then reply "WTF" or something similar and your friend then asks "Hello? Is this Lauren? I've got through to the right number yes?". She'll then reply "no, wrong number" and he then asks "Oh, who have I got through to then out of interest? What's your name then? Can I check that number again?". Basically try and social engineer it so that she doesn't feel threatened into giving her name, just to confirm it's the "wrong number". Very stalker-like but it might work.Option 3 - Google her based on what limited info you might have. Probably won't work though. Do you know where she works or anything that might help you find related info? Option 4 - Blag it for a few weeks... just call her "hiya" or something until you see her pay for something.Option 5 - My second favourite one - Give her a missed call from your home landline (NOT your mobile). Let the phone ring twice or something then hang up. When she calls you back, ask "Who is this" or say "The line's really bad... I can't hear you... who is this?". With any luck, you'll then get the confirmation you need. If you don't hear it the first time around, say "Can you repeat that? I didn't quite hear". Do Option 1, then Option 5.