not receiving imessenger when switching 3g on
when i am in the middle of an imessenger conversation and my phone is on 3g, then i go into the settings and switch 3g off, there is little delay of 2 minutes till imessenger receives again.
however, when i am on 2g in the middle of imessenger conversation, and i go into settings and switch on 3g, exit messeges and lock the phone and wait for up to 7 minutes, the phone doesn't receive the remaining imessenger conversation untill i unlock the phone and go into message.
i have iphone 4 running ios 6.3.1
why is that?