I had this problem on my network... I know that notifications work, prefix is just "!" but when I did that, nothing happened... Then I went abroad and when I was in roaming, delivery worked like a charm... What I did is that I took another Sim card from same operator (I came in my home network) and it was newer that this not working... I surprised when I found out that everything was working perfect. I started a Bugzilla for this and in meantime discovered "solution"
Cheers