I have just had the same problem in the last half hour. I have tried to FaceTime my daughter won't connect also have tried the iMessage (green blob) that won't deliver but email will. Just got an iMessage from her whilst I am typing. No idea why facetime would not work though.
Really didnt want to update to ios7 as alot of my friends that did have had problems its seems as if the I phone 4 is not up to using newer versions according to friends lots of little things goin wrong but guess I will have to find out for myself and update trouble is you can't go back to ios6 once you have updated