Because you haven't updated.... A little obvious. But can explain what's the problem?
For crying out loud......
Instead of bitching at each other and/or making assumptions, how about somebody try and help the OP?
Enter *#1234# in the dialer keypad and post the three lines displayed here. That will tell us your current firmware version.
Weird. I thought when 2.3.6 was released, everyone would have gotten it subject to regional release. If branded UK phones had 2.3.6, that must have meant Samsung already released 2.3.6 to carriers, which meant it must be available (somewhere).
You think carriers can prevent release of 2.3.6 from Samsung?
Simpler for me, either have or don't have and pretty sure the updates are available for everyone regardless of carrier/contract. Telcos here just don't have the expertise to create bloatware so the release goes to eveyone when available from Samsung, contract or not. Or maybe because we skipped 2.3.4 and 2.3.5 that's why had 2.3.6
so i just be able to get 2.3.6 somewhere mate?