Given a list of unknown shipping carrier tracking numbers, how do I
conclusively identify which carrier a given tracking number is for?  I
need to know for at least the 4 major carriers: UPS, FedEx, USPS &
Airborne.  Any others you may have info on are welcome.

General answers like "12 digits is probably FedEx" don't help me.  I
need to know for sure -- ideally there would be some sort of
check-digit or something definate.

Here's what I've been able to glean so far:

* UPS Tracking Numbers appear in the following formats:
  1Z 999 999 99 9999 999 9
  9999 9999 999
  T999 9999 999

* Airborne tracking numbers may be up to 11 digits.

* FedEx Express are generally 12 digits.

* FedEx Ground are 15 digits.