Somtimes the number int he caller ID has a different format (somtimes it includes the area code somtimes it doesn't, somtimes it includes the carrier selection code and somtimes it doesn't etc), somtimes it does find a match in my contacts, but somtimes when i thought it should find it doesn't i'm not sure why.

What are the rules for matching the number reported by the caller ID to numbers in my contacts? And would there be a way to customize those rules?