Normally the product code is like:
MC603 = model number - which product you have
KS = language like the Keyboard, PowerAdapter ... in the MacBook (Pro).
/A = revision of the product
In the iPhone software the /A revision is hidden, so when where is "MC603KS" it will be a MCC603KS/A. Actually there is no iPhone with "M...xx/B".
MC603KS is the iPhone 16GB black sold in Sweden. According to this list every iPhone sold in Sweden is locked to a carrier?
According to the Apple Online Store Sweden, Apple directly sells unlocked phones.