It appears that you are installing and running this on each desktop. This is highly inefficient a slient server model would be a lot better as this would decrease the workload on the desktop machine.
The simplest way of doing this is using a database and you get the performance benifits if server caching index.
Your current code appears to do a straight string match similar to a like. Indexes are not as good as handling these kinds of searches as the whole string is not matched. If you are matching a complete sting an index is very fast.
If you need fast lookups on partial numbers you might look at either reverse indexes that sort based on the digits in reverse order or preprocessing the numbers and extracting sequences of digits and then indexing them.

UnderMine