What component determines The Network / unlocked?
What actual part of the iphone holds the information if its locked / unlocked and even imei number???
It depends on which iPhone you're talking about. Up until the iPhone 4, all models were GSM only, which meant that it had to be a carrier with a SIM card (AT&T and T-Mobile, here in the states). Starting with the iPhone 4, however, the ICs on the communications board determine whether the phone is CDMA or GSM.
Locked or unlocked is another beast altogether. If you have a phone that is locked to a carrier, you may not use it on another one. For instance, a locked AT&T iPhone will not work with a T-Mobile SIM card. Similarly, you cannot activate a Verizon-locked iPhone on your Sprint account, even though they're both CDMA. Phones are locked so that a carrier can keep your business over the course of a 2-year contact, which is why they're able to sell you a brand new iPhone for $200 instead of $600.