T-mobile / GSM phones - what do the lock statuses mean?

[AndroidSPCS]

On my Vibrant, there are several lock items:

Network Lock
Network Subset Lock
SP Lock
CP Lock

I think the Network Lock is to lock it to a carrier (eg T-mobile) only. Please correct me if I'm wrong.

What is Network Subset Lock, and what are the SP / CP locks?

I tried googling but have not found an answer to what these locks mean.