What happens when you receive a mobile number with a missing digit? Try to interpolate, of course!
You're out of luck if the missing digit belongs to the lower end since that's where they're relatively arbitrary. It's only at the higher end that they tend to be more structured and predictable. But how do you know where the absconding number originally belonged? If it's a high-end 9, it's child's play. If it's the digit directly after that, and you're aware of another number from the same locality, you're in luck once again.
That's what I did today and it worked. I'm not a total telephone tyro after all! Social networking and stocking all those continually piling numbers can be beneficial in more ways that generally believed.