I've been having text trouble with o2 today as well, as has my mum. I dont bother stressing about it because a) why bother its o2 b) it will be back eventually.
The big problem here, that not everyone knows, is that ( and i believe this is still the case ) o2 let " 3 " use their network, in fact i once read that 50% of the o2 network is used for " 2 " alone, so it's no wonder we o2 customers always have trouble. When you have problems like this it's usually probably down to the network going to or a backlog of texts stuck around the system.
You know what though o2 really shaft us because we can still get charged for sending texts even when the network goes down, and in order to test it to see if it is back up we need to text again, thus incurring a further charge, it'd be nice for the con merchants within o2 to actually give us that ( our ) money back. Never happen though.