How to search for a part of a number

Hi,

I'm wondering if there was a clever way to find parts of a numeric
string in another table.
There is a table that holds city-codes and city-names. City-code would
be the part of a phone number that identifies the city.
Over here this code can have 2 - 5 digits. So the table would contain:
23 ; A-City
345 ; B-Town
4455 ; C-Village
632 ; D-Town
...

I'm quite sure the numbering system is bound to be spanning a search tree.

So there are 2 tasks:
a) I'd get 445598765 in and like to know the corresponding city
b) I'd like to get the number nicely formatted : 4 4 55987-65 -->
4455 / 98765

Obviously one could do it on the client side.
As I dont know how many digits in the input are relevant, I need to try
the shortest code first.
1) search for 44
2) add 5 and search for 445
3) add the 2nd. 5 and search for 4455
BINGO

Is there a way to do it within the db?