I am continually having this problem. I send an SMS, put my phone down, and think nothing of it. Then, after several minutes (5-10), I unlock my phone because the people I text usually reply quickly. I navigate to the Messages app, and see "Sending..." at the top. As soon as I see this the message sends. It is almost as though me going back into the app causes it to actually send. I have signal/service just fine. I have experienced this at least 3 times, with three different contacts, all of which have different cellular carriers. It has occurred when I am in physically different locations: school, outside, house etc. What in the world is going on? It is incredibly frustrating because I keep apologizing to contacts for taking 10 minutes to reply to them. Anyone else seeing this?