unless you work for the Police then its kind of impossible to get a name from a mobile number. You could have a pay as you go sim card with no registration to the person using the phone so thats why its hard.
If its a contract phone then they are protected by the data protection act and only a court order can overrule this.
If you have access to the database where all out details seem to be floating around the ether everyday being sold to every other company with a large wallet then you in luck.
Sending a text to the mobile with something like "hey john you were hot last night" might do the trick, they will only be too willing to send you packing by saying their real name to get their angry girl friend off thier back lol
that last one might not work, however use your imagination. :)