Hi there, I upgraded to a 5s a few weeks ago because I was having this SAME problem on my 4 and I thought getting a new phone would solve it: Sometimes, it will take up to 20 minutes for my phone to receive an imessage. When it finally comes in, I can see that it was supposed to be delivered forever ago, but am only just receiving it. That is happening when I am sitting at home on wifi. Additionally, I have noticed that I will not receive a text from someone on an iphone if I am not on wifi or data. I get bombarded with imessages that I was supposed to receive when I do connect. It's like it doesn't default to sending them as texts if not on wifi. Any thoughts? Thanks in advance, this is getting frustrating!