Telco sets have firmware customised with Telco apps. Each Telco has their own CSC code: SIN MM1 STH. XSP is the non-Telco code. Basically, if you buy from Samsung retail shops, the phone will have XSP code.
In addition to no Telco apps, phones with XSP code will receive updates faster than phones with Telco codes.
Enter *#06# in the phone dialer to obtain the IMEI number (14 characters) for the device. You can then enter *#272*Device IMEI# to select a CSC code
Caution: Changing CSC code will wipe out your phone. Do a backup before changing CSC code.