OS's are device dependent. Assuming you don't have the latest OS, then the 8310 sticky thread at the top of the forum will be for you, regardless of the Carrier.
Enter your PIN and it will let you know if there are any updates available fro your BB. This will be the latest carrier approved OS for your BB, so it won't necessarily be the highest OS version at the top of this forum, but it will be the latest approved OS for your carrier.
You can find your PIN number for your device by checking Options > Status, or Hold down Lt Shift, Alt then press h or type mypin in any text field (memo pad, etc.)