If its not a network related issue then the problem could be from device itself. As Samsung Galaxy S2 has a built-in spam functionality in messaging.
So inorder to verify the same, just try sending sms with any another device on your S2 and just see if the other device gets a delivery confirmation report or not, if it does, and you still don't receive that sms. Then in this case you've unknowingly/accidentally switched on the spam function your Galaxy S2.
Follow the instruction below to unblock your incoming SMS
Using the Settings menu
- From any Home screen, tap Messaging.
- Tap the Menu key.
- Tap Settings.
- If necessary, tap Spam settings to select the check box
- Tap Unregister number as spam (if any)
- Touch and hold on the desired number and then tap Delete
- Tap OK
Hope this would resolve your problem :)