Thanks ladies. I found it :) It was hidden in my sons crib under the pillow. He must of taken it when I wasnt looking. Oh well...did major spring cleaning today as a result of it so maybe it was meant to be ;)
DH had his phone stolen from my car a few years ago and the police managed to retrieve it by tracking its serial number. I'm not sure if they'd do that if you lost it, though! Might be worth asking nicely?
The only suggestion I have is to try ringing it, but I guess you've tried that already. The last time I couldn't find mine, I eventually remembered I had given it to someone else to speak to the caller I had on the line and she hadn't brought it back to me.