Why is iMessage not working?

Today all of my texts were taking forever to send, and I mean a long time. It finally said sending failed and reverted to regular text message instead of iMessage. Why is that happening? Why is it going so slow when I text other people with iPhones? I did a software update and it is still doing it and it's not like these people are far away. Does anyone else know how ti make iMessage go back to normal?

Added (1). The Wifi is connected so I don't know what the problem is. I can only use the regular SMS not iMessage.

Are you sure your data is working properly on your phone? IMessage requires an internet connection to send and receive messages.

It's out for a lot of people and it's on the apple side.

It's not just you. I was having the same problem on both my ipad mini and iphone 4s and I reset them both, but to no avail. Apple is having problems today. Let's hope it gets fixed soon.