iMessage issue in detail

I've seen numerous iMessage threads but none seem to explain the exact same issue I'm having recently.

I have just got the iPhone 5, however this was present on my iPhone 3GS on iOS 5.0.

Randomly when I go to send a message it will do one of the following.

1) work as it should

2) show up as a green message and refuse to go blue even if I turn iMessage on/off. It will only allow me to send blue once and ONLY once that person has texted me. This person has been in the same environment as when it wouldn't allow me to send it. As in at home on wireless or on 3G with full signal. It just won't work till they send me something.

3) sends as blue (iMessage) but the person does not receive it, again, until they text me.

I know this has also happened on other phones as my girlfriend also expierenced this on her 4s, and not just me but from other people aswell.

In short, this only started in the last few months, happens on 3GS/4s/5 and has happened on at least 5.0/6.0.

The fact that I simply don't receive or other people don't receive messages is a little worrying, has anyone else expierenced this? I have three different people having, one is in the U.S so it's not limited to just UK or UK related networks.

Thank you in advance to any replies.