"Service nos." what is it?

Hi.
In Nokia 3310 phone book directory there are have function named "Service nos."
What is it? WHat is need?
Thanks

as the 3310 doesnt store numbers in the phone then these service numbers must be on your sim card i think.

if its what i think it is then they are the numbers for you to connect to your service providor for top ups/inquieries etc.