I find it funny how many people do things without checking facts... 0 or 1 are about the lowest class you can get...
To quote a spec: Ordinary cellphone users have numbers in the range 0 - 9. Higher priority users are allocated numbers 10 to 15 [1]. During an emergency, some or all access classes in the range 0 - 9 are disabled. If the overload condition continues, mobiles with access classes level 10, 11, then 12 and so on may also be disabled by the operator.
Normally it should match the last digit of your phone number and for the most part isn't used any longer.